You are probably right, but this issue is not specific to me. Everyones' legs run from the ground to their crotch. Bottom bracket is x cm from the ground. Seat height should also be about x cm if the TT is up to bone. Now, I do prefer my leg extension to just short of the knee break. That's probably a result of years of distance running.
Bob,
Bottom bracket heights can vary widely, for example a 54 cm seat tube could differ in 'standover height' by as much as a couple of centimeters.