What does the OOP range look like?

My guess is it could be doing this against an overly weak range, allowing it to bet more middling hands that want to get thin value/deny equity from a hand like AK/AQ/AJ

Agree with Ryan - I believe Pio doesn't want to split its range, leaving its small bet or check back range less protected. Pio uses the advantages IP has to allow them to over realise equity with their full range rather than going thicc with one part and playing other parts differently

Same deal as with a lot of boards people simplify to 1/3 on in SRP IP vs BB; because BB can't check raise effectively IP gets to bet everything. I believe splitting range allows BB to check raise vs the small bet and solver calculates that more EV is captured overall by merging

First,

You are betting with a hand because ev of bet > ev check.
If no hands bets bigger, it because against vilain s optimal response, no hands have better ev to use a big size rather than a smaller one.

~ 3 hands classes here :

Flush

2p set

Air, or Ad , Kd.

Flushes can go all in on the river anyway. Imagine you have A3dd. You are going to stack vilain if he has a flush whatever the action you take on the turn. So these hands benefits to use a small size to target hand like, weak pp, one pair hand , Kd type hands.
So flushes have no incentive to bet big. If you have a low flush he is gonna call you with a too strong range, If you have something like A3dd , you want him to have a « close call » with Qd Jd.
Pio preferes to target weak hands from vilain s range on the turn, in order to put a lot of hand in vilain range indefferent by calling or folding.
We are shoving the river 2.5x in order to maximize ev with our strong hands.

2p set, and str8 :
if you bet too big, you are going to isolate you agaisnt flush.
These hands benefitca lot from X or bet small. It targets hand like KdQ, be call by all the ovp played this way (not so much), and hand like AQcno diamond.

Air or one pair hand :
These hands don’t want to be isolate agaisnt a « strong range », benefit a lot if they can have a fold from a hand like AJo, ATo. (Don’t say these hands are folded 100% , it’s just for the example).
KQ, KJcc. Also, I guess they have a better R by betting small.
If you have a hand like Q9ss, you don’t want to bet big, and your hand benefits to generate fold from hand like JTcc for example.

Hope my explanation was clear. Keep in mind that we are not sacrificed Ev with our strong hands in order to protect our weak hands. Solvers don’t operate like that. If with a nutted hand, ev big size >> ev small size. The big size will be chooses near 100% of the time with his hand.