Flop is A87 with a flush draw; hero has none of either suit.  Villain bets 1/3 of pot; hero calls.  Turn is an 8, putting a second flush draw on board.  Hero bets 70% pot.  River is a 7  (not a flush card), hero bets 1.5x pot.

What does PIO do here?  Hero never folds flop, but does a fair bit of check raising; 14.4% of range, and 26% with his actual hand.  

On the turn, PIO basically never donks.  However, I reran the sim with hero not allowed to check raise preflop, now PIO donks about 25% of the time.  PIO doesn't like it when you limit its options, like no check raises on flop.  Making up for some lost time, now it bets.

On the river, as played, I gave PIO multiple bet sizes.  Interestingly, it prefers either a smallish bet say 1/3 of pot, to get folds from Villains missed flushes (KQ,KJ, etc.) that we are chopping with.  Or, it uses a large size as hero did, targeting Villains Ax hands.  

This is something I have seen a lot; not sure if I posted this here before.  PIO tends to avoid medium sizing on the river.  Either polarize, or go smallish seems to be its preferred sizing.  

Just as calling is not a good compromise (Thanks, Andrew), using a middling bet size isn't either.  You want to have an idea of your bluff targets and value targets and size appropriately.  One caveat, this assumes we are playing PIO.  Many Villains will look at your bet in absolute (dollar, or chip) amounts and NOT in fraction of the pot terms, as we know they should.  In that case, something like 2/3 pot might seem 'big/polarizing' when it probably shouldn't.