i would find it impossible to put him on a flush draw, especially with the Ah on the board. solid players pretty much aren't reraising KQs from the SB...i think the risk of giving a free card on the turn are minimal, and outweighed heavily by inducing another bet (or a check-call) from AK.

something else to think about is that the raise and check-behind on the turn is a play that i would make if i was the one holding the strong flush draw.