Theoretically, balls and strikes are based on where the ball crosses the plate. If the ball cross the plate knee-high and over the plate, then takes a dive into the dirt right after, it should be a strike. Not everyone understands that, however. Umpires shouldn't be relying on where/how the catcher catches the ball, but if they never did we wouldn't spend so much time teaching catchers to frame the pitch.
What I've never understood is why some umpires have such small strike zones. Not good ones, of course, and certainly none who are members of DFP. But some just don't seem to like to call strikes. You would think it was in their best interest to call them since no one wants to see a walk fest and the game will take longer if you're not moving it along. Maybe it has something to do with time limits, since there's no penalty of staying longer if there are fewer outs. Still, no one is going to be happy on either if pitchers aren't allowed the corners, even with the whole ball on. So why do it?