Your operating technique (leaning, power settings, flying in balance etc) is more likely to affect available endurance & range than the limited amount that would spill or overflow.
If you're really curious about it, run the tank dry while the aircraft is in a level position on the ground and then fill the tanks afterwards. Even though the ground attitude is likely to be a little different to in-flight attitudes it's not likely to be significant given the range of possible straight & level pitch attitudes.