So I just started digging into bvb 3 bet pots. I've looked at CO vs btn 3 bet pots pretty extensively.

I use solved preflop ranges

I expected sizing patterns in blind vs blind 3 bet pots to be similar to CO vs BTN 3 bet pots. However, they're very different.

SPR in SB vs BB is different (bigger), so I enlarged the SPR in the co vs btn boards, but it didn't change the bet sizing choices.

Board I looked at:

KT4

CO v btn cbet sizing choice:

33% pot, basically a range cbet

BvB cbet sizing choice:

When given a choice of 3 different sizings, big blind prefers heavil the largest size I gave it (75% pot), rarely using the other sizings.

Boards like Q52r, K94ss, T65r etc also prefer larger than half pot sizings which I was surprised by

The only class of boards that we actually prefer to bet small seem to be (not surprisingly) monotone boards, a minority of ace high boards, and higher paired boards.

Anyone know whats going on with the ranges here? Why we want to bet big on these board types with these ranges vs the CO and BTN matchup ranges?

BTN 3bets linear vs CO ; BB 3 bets Polar vs SB. BB has less advantage deep within the ranges because of all the crappy hands. that leads to a larger, more polarized betsize on the flop

In a single raised pot co vs bb, the co opening range has a lot of junk in it (but more middling hands than a bb 3 bet range), and the bb call range looks fairly similar to a sb call bb 3 bet range. Yet in the former case a third pot sizing would be used

To experiment I increased the SPR of the bvb 3 bet pot on K92ss to 20 (similar to a SRP). Now the 33% sizing is used 20% of the time compared to something like 2.5% of the time previously. The big size is still mostly used.

So i guess it's something to do with the bb having a lot of complete trash

So the problem with just changing the SPR is that the "definition" of a Nuthand changes. With a lower SPR Overpairs and strong Top pairs a part of the "nuts" that allow us to use larger bets. with a high spr these hands become middling strong hands. dominating villain in the nutrangepart leads to big bets and dominating villain in the middling strong range part lead to smaller bets.

Also i would not say that CO is opening a junky range... it is wider but still pretty linear.