Let's say I am in an EP seat at a full ring table, (but not UTG), and I have JTs and I might normally raise this to 2.5x in an unopened pot and I perhaps expect to make a small amount of money doing this.

Now lets say I am still in EP and there is a limper in front of me, and I have JTs, so apparently now I can 'raise large to punish the limper' and so I raise to 5x and hope this to be +EV for myself.

In both situations the same players are left to act behind me.

Why does the presence of the limper allow me to 'force' my hand of JTs to be even more profitable now with a 5x sizing, when it was barely profitable for 2.5x with the same players behind? Why can't I just raise JTs to 5x from the outset without a limper, (along with other hands in my range)? Why do I need there to be a limper?

The other issue I have with 2betting to a large size is that you can allow players behind you to 3bet you at a better risk/reward ratio for themselves. For example, if I open to 2.5x, an aggressive player behind might 3bet me to 7.5x or 8x, but if I go to 5x, he can 3bet me to 13x and force me to fold the weak parts of my range as they can't call an extra 8bb OOP. So by going large, I help the players behind me right? Plus they may 3bet me even more now, whereas when facing my 2.5x open, they will flat some hands, when looking at a 5x open, they may 3bet their full range which really hurts the bottom of my range now.

So yeah, aren't the players left to act just as much a factor in everything as we are still playing poker against the whole table and not just people that have acted in front of us right? We don't want to play in a way that makes us lose money more easily to those behind us surely?

I'll take a stab at your question based on my understanding.

You should theoretically be tightening up your opening range both if you choose to use a larger opening size and ALSO when players have limped in front of you. So in your example if JTs is a marginal open for 2.5x from early position, then it likely becomes a fold when faced with a limper.

You can think of your opening range as kind of a sliding scale that changes based on your opening size, with larger opening sizes necessitating tighter ranges. Somewhere on that sliding scale is the optimal point where opening size and corresponding range maximize returns, but I am not aware of any current consensus about where that point is.

Based on everything I have studied from high level players, you can likely achieve a similar winrate with either a 2.5x or 3x open, but if you choose to go with a 3x open you should be opening less hands. I think most players choose to open 2.5x because there seems to be a lot of available solver work/training at that size and also because it allows you to play more hands profitability, even though you may be profiting just as much with a 3x open while playing less hands.

As for limpers, based on the solves I have studied you should theoretically be drastically tightening up your range in response to a limper, especially from late position where you could normally open a lot of hands profitably when it folds around to you. One limper makes many of your marginal profitable opens turn into folds.

However the reality is that most limpers are fish, and in that case opening larger with a wide range (like in your example) is an exploit to try to isolate the weak player in position, knowing they will make errors postflop that result in profitable spots for you. This opens you up to counter-exploitation, especially from regs yet to act, as you alluded to.

In the games I play in this dynamic is the main driver of the action... Weak player limps, reg attempts to isolate, second reg then 3-bets to take advantage of the dynamic, forcing first reg to either tighten up their isolating range or 4-bet more, etc.

Sometimes the potential gain of isolating a bad player with a 5x sizing is so large that you make more the times you get heads up than you lose when you get 3-bet and have to overfold. Just be sure to adjust. If you're getting 3-bet every time you open you have to likely tighten up and/or 4-bet more to combat players 3-betting with too wide of a range At least that's the way I approach it.

You're getting common exploitative wisdom and theoretically correct play mixed up. Of course it's not theoretically correct to raise 5x with JTs vs an UTG limper. In theory JTs probably wouldn't even raise at all in that situation. People do it in practice because limpers are bad passive players and they expect to make more money that way (though it may very well be the case that 5x is an incorrect iso size even from an explo pov).

Your intuition about raise size vs players left to act is correct though. The more players there are left to act behind you the smaller your raise/3bet size should be.

I think online raising limpers is even worse because most of the time they are a passive fish, but probably 20% of the time they are a bad reg that is looking to limp/reraise with AA and KK, meaning that you lose all of your 5x open when that happens. This probably occurs occasionally live but less often I would imagine.

So this additional factor makes raising limpers even less profitable so online in particular we really should tighten up a lot more.

Some of the hands that you would normally open in a given position might be better to overlimp after a limper, rather than raise and try to isolate. I'd guess that the JTs in your example is one such hand, but I could be wrong there.

But the bigger point here that has been overlooked is that the presence of the limper removes some hands from your raising range, mostly the weaker ones, IF you have an overlimping range.

This in turn should strengthen your raising range, which would justify a larger sizing for it (but maybe not the 5x suggested).

The commonly seen strategy suggested by the OP seems like an abuse of this concept, because the 5x range has NOT been strengthened by the removal of its weaker hands.

If I do see over-limps from regs online, it is typically from the CO and BTN with suited connectors/gappers, suited aces and small pairs. I very rarely see regs over-limp in EP and MP.

How can there be a limper and the same players left to act at the same time? If someone limped right before you then there's 1 player more left to act.

You are arguing semantics as I think it is fairly clear I am referring to the players that are yet to act at all in the hand so far.

There is one player more left to act, the situation is not analogous to open raising. If anything, the situation is more analogous to 3betting.

The reason you (can) go big and wide is because the guy is a baboon and you don't want other regs to get in the hand. Also fishes are inelastic so up to a certain sizing they will call the same hands.

Raising limpers is honestly where most of your winrate will be generated

Why is this?

The pot is now 2.5bb, but you are never taking this pot down pre-flop if you raise to a reasonable sizing as the limper has some kind of hand that he wants to see a flop with.

Surely your bb/hand is worse in limper hands because of this, as you have no pre-flop 2bet fold equity?

I agree that the limper is good for any potential 3bettors that are acting after our 2bet, as that limped 1bet now counts as extra dead money a good chunk of the time.

Weak limpers at our table is good overall, but that is when they call our open 2bets and 3bets with weak hands. The hands where they limp in and call a 2bet, and we specifically are the 2bettor, I find that we don't win as much money per hand as when we raise first in with a 2bet, as in the latter example we can win 1.5bb/hand when everyone folds, but this doesn't happen in the former as the limper will fight us for the pot with hands as strong as TT and JJ on occasion as well as his weaker stuff, and this hurts our EV.

A simple example to illustrate my point is say we open raise 87s on the BTN to steal the blinds then this will likely be higher EV than if we 2bet a limper when we are on the BTN with 87s.

Yes, open raising is in general higher EV than isoing from the same position with threshold hands. But isoing is extremely high EV with a good portion of hands, assuming you play them correctly postflop. These players will allow you to win at insane winrates whenever they go postflop with you, since they play in very predictable ways.

If i'm understanding FFP correctly wouldn't that just lead to making giant ass RFIs from UTG and HJ.

The goal of an isolation raise is exploitive: we want to get heads up, in position, as the PRF, with bad players who pay our value bets too often postflop. Our larger raise size serves to discourage 3bets slightly and it inflates the pot when the limper calls with their capped, juicy, wide range. We do need to be conscious of who is behind us as it sucks when we get 3bet here. This play works best when the players behind us, who will have position on us, don't 3bet enough. So it's a great move on the button or the cutoff.

Surely it is the opposite, where it encourages more 3bets?

For example maybe the BTN might normally when facing a 2x-3x raise size from us, he may choose to 3bet us with a 6% range and call with a 6% range. However if he is now facing a 6x raise from us, he may choose to 3bet 10% and call 0% for example. Overall he continues less but with a 3bet more, denying us equity more often with the bottom part of our range.

I went and looked at some GTO tables for different initial raise sizes. The answer to this question is interesting and nuanced. With a larger raise size, the initial raising range tends to come in as a bit narrower range and it gets 3bet by a slightly narrower range. However, most "facing an RFI" GTO ranges are highly mixed strategies when the potential raiser will have position, so most hands in the range raise some and call some. This raise-call mix shifts for most hands in the range shifts to more raising as the initial raise size goes up. However, a few hands drop out of the range, and this makes the aggregated 3bet% go down slightly, at least in the one example I could find.