Xaston,
i also think villain will sometimes show up with KQ/KJ. in a vacuum, i will assume that the average 18/6 player at $1/2 NL doesn't play position very well, and will be roughly 18/6 from all positions.
my theory is that the value gained against one pair by playing KK this way is greater than the value lost when villain finds a fold on a
river with a set. i think this type of villain lays down KQ/KJ to a turn raise almost 100% of the time.
im a little too tired right now to actually do any EV calculations, but i want to clarify that my thought process did include thinking about villain folding on a flush river. i did some quick estmates about weighted ranges and assumed that villain would fold KQ/KJ to a turn raise 80-90% of the time and would fold a set on a
river infrequently but sometimes.