You have said this player has been putting in substantial raises with pair plus flush draw types hands. So, we can start by considering if he has turned the nut flush, which means he would have flopped top pair and a flush draw. Is this a hand that he would have raised you with on the flop? Does the size of your flop bet make it look weak to him and make it more likely that he would have raised? By thinking about how he would play A
x
, it is possible that you can discount or even eliminate the nut flush from his range.
Your next step is to look at the K
x
hands in his preflop limp/calling range. You block his ability to have KQ/KJ. Would he play KTs that way preflop or would he have raised? Would he have played worse kings that way?
Would he raise you with smaller flushes? It feels like the answer is yes. Would he check to you and risk giving a free card? I have played against opponents where I could rule out made but vulnerable hands because they are too scared to go for a check-raise because of fear that it gets checked through.
Would he have slowplayed or made a smaller raise if he had a bigger flush? If you think that the answer is yes, that makes it very like your hand is good.
Would he raise with a made hand that is not a flush? It's possible that you can rule out flopped sets and two pair because, as with a small flush, you might assume he would either check-raise or lead out to avoid a cheap turn, so he might have a hand like A5o with the A
.
Will he interpret our turn bet size as weak or will he think we might not always c-bet a flush draw on the flop? This makes it more likely he might jam with the nut flush draw on the turn.
These are the questions you can ask yourself at the table to narrow down his range. How you answer could make this an easy fold or an easy call. It sounds like you have played with him enough to at least guess at the answers.