[Buzz]

uberpron - In theory, when you flop middle set, the probability any one of, for example, your three opponents who have seen the flop has top set is very approximately three times the probability one opponent flopped top set. Assuming no bias by any opponent who was dealt cards for or against the high pair that would have flopped top set, and also assuming you don't have a card the same rank as the top flop card, the probability any one of your three opponents flopped the nut set is:
6*42*41/2/148995=0.0346723.

Very crudely, since that number is fairly small, we multiply by the number of opponents who actually saw the flop to estimate the probability any one of them flopped a set, and then we round down a bit to maybe two digits.
Thus 0.0346723*3=0.1040169.
And then the probability one of three opponents has flopped top set is roughly 10%.

Then if UTG is the one who bets, and if the others fold, I think you presume if anyone made top set, then it was UTG. Thus the probability UTG has top set is approximately 10%.

I think 10% is a pretty good ball park first approximation for the one who bets having top set if three opponents have seen the flop. You refine that on the basis of your knowledge of tendencies of the bettor. Something like that.

Buzz