Just for clarification, BB drop has no relationship whatsoever to wheel and tire size. It's the measure of the BB center distance below the line created by connecting the centers of the wheel hubs (dropouts). BB distance from the ground, OTOH, is a function of tire radius minus BB drop (as mentioned above).

For instance my old KHS 26" MTB had a higher BB than my 700C road bike. Its BB drop was very small in comparison to the road bike.