[PLO5] A-High Flush, paired board on river - check behind?

You don't say what limit this is, but where I play PLO, the turn would be a pot-sized bet.

OTR I think that if villain hit his boat, then a small bet to induce a bluff might tell you he did.

With that in mind, I would bet something decent (I use 2/3 pot, but only because my client is set up that way), and I sometimes fold to a full pot raise, and sometimes call depending how villain has behaved before.

Cheers,
VS

OTT As a default it's theoretically right to bet pot as standard as vorpal said because with his sets he has decent equity to a fullhouse you dont want him to make a correct call. I personally have 2 sizings here: 4/5pot and half pot. 4/5 im repping the nutflush, semibluff topset and bluff the nutflushblocker and set up for a big bet on blank rivers. Against strong regulars if I recognize they adapt, Im also mixing in some of the nutflushes into my halfpot range so I protect my 1/2pot-1/2pot flush value ranges with some nuthands to protect it against players that might catch up. Against weaker players 2/3-pot everything makes sense you need to get a rough poicture which hands they pay off and how often they have those.

OTR you make a small token valuebet here of 1/4pot to get value from non-nut-flushes and maybe trips. If he is capable of encountering this better just check behind.

Bet turn a little bigger, and bet river 2/3 pot. If he raises river you happily fold.