From what I learned in the beginning stages of my poker career, we should raise larger in Early Position and smaller in late position because

-EP range is stronger, extract maximum value
-Larger raise size helps to isolate players and thin the field, more important with more players left to act behind you
-In LP, you can keep the SPR higher, allowing you to utilize your positional advantage more (don't think this is too important personally but it was brought up by many video producers last time)

MOP page 268 states that
1. When our opponents have a strong hand in the field, they will likely reraise or at least call.
2. When no one behind us has a strong hand, it will be typical that the pot will be contested headsup between the raiser and the blind.

In choosing a raise amount, we will want to strike a balance between these two scenarios. In the first situation (where the opponent has a strong hand), we generally want to keep our investment in the pot small. In the second scenario, we want to make our raise amount appropriate to put some pressure on the blinds while extracting the appropriate amount of value.

...

That means that our raise size should be varied according to the strength of our distribution, and as our position becomes later and later, we open with weaker and weaker hands.

...

We want to open 2BB in early positions and open 3BB in late positions because
-Fewer players left to act -> Someone shows up with a strong hand less often -> We don't have to fold so often to a re-raise.
-To achieve the effect of putting the same amount of pressure on BB with a wide range of hands in BU as compared to a strong range of hands in UTG, we need to raise larger.

I could have some counter-arguments for this though:
-When you are in EP with a stronger range of hands, you just show up with more hands which can continue vs a 3bet
-You get 3bet more often in late positions. The blind might have a top 5% hand less often, but he'll widen his 3b range accordingly if you are opening wider.

I just found this really interesting. The old school of thought definitely makes sense from an exploitative standpoint. I wonder if opening smaller in EP and larger in LP makes more sense from an optimal standpoint. Thoughts? I know a lot of bots are opening 3BB. It's regaining some popularity at mid/high stakes and some top level players have started re-using 3BB raise sizes again as people start being able to defend really well in BB

None of my theory posts ever get answered :S

TLDR Version:

Typically, people open 3BB in early position and open 2BB in BU. MOP suggested the opposite. Thoughts?

Could be that multiple sizes are optimal, and use different ranges(worst hand in each range benefits from that sizing).

This is interesting. I think the most important thing to considering when thinking about raise sizing is the type of opponents behind you, but i never really thought about position directly effecting raise size pre.

I play live, so this will be easy to exploit.

Thanks for the info, chip

i guess multiple sizes are probably optimal, but impractical for humans to use.

for opening range, it stays same or inverted?