I don't think it does though. Let's face it, you're not pushing your dick through a hole in a door (well, maybe YOU are). You're pushing it into a woman, and her ass/legs/labia/pelvis/etc are all blocking you to some extent. If you're fat, that's FO' SHO' going to stop some penetration.
Actually, guys should be measuring from the tip of their bellies to the tip of their dicks. I bet some guys here would have a NEGATIVE measurement.