Let's assume the strike zone is like the rectangle K Zone we see in Baseball.
When you differentiate the highest shoulder, every ump I've ever asked about it assumes the front shoulder is the highest. Let's be real, they're not checking the batter between each pitch to see if they're shifting. Most of the time our umps don't even notice if they change their position in the box at all. Making it back shoulder just makes that easier for the ump.
Back to the point though,with highest shoulder, that rectangle is vertical. With it being the back shoulder it lays back at an angle. The pitch is coming down at the opposite angle, so it opens up the possibilities for me to vary speed, arc, and height much more and pass through that rectangle.
The bottom of both strike zones is cut off by the plate. You actually lose more of the zone there with the laid back, back shoulder zone. You make it up on the back end though. I pitch off the back of the rubber, so it's even more exaggerated for me than someone pitching off the front. It's geometrically possible for me to throw a ball 10' in the middle, passing through that vertical zone, and missing the plate, but just barely. It's like a carnival game at that point, and ridiculous. It may only be possible to the left and right notch as well. The tip might prevent it entirely going right down the middle.
While we're on the subject, if you imagine the strike zone like those K zones on TV, is any part of the ball in that rectangle supposed to be a strike, or does the entirety of the ball have to pass through that zone to be a strike? The reason I link this subject here is because in my 15+ years pitching, it seems the umps err on the side of caution all the way around. They won't call anything that's close to 6' or 10', if they call corners they only call a ball that has maybe 1/4 of it's area outside of that rectangle, and only if it lands in a non-controversial spot.
I really hope UTrip gets their Arc problems under control. This arc is up and down crap they are trying to emphasize is complete junk. I don't care if that's how it's written, then it's written poorly. If I release a ball at 3', then the ball can't cross the batter any higher than 3' to be a strike. That's asinine. I can't attempt to disguise my pitches at all. Can you imagine FP telling a pitcher they can't throw a rise ball for a strike because it doesn't drop? That a sinker is only a strike if you start it at a certain height, even if it crosses through the strike zone? Arc limits are to keep us from skying it and throwing a modified pitch, and their whole arc definition is just making something people have enough trouble understanding, needlessly complicated.