So is the X dimension measured at the prop shaft or the engine crank shaft? I remember reading the review for the Donzi 22 Shelby and they said that the larger hatch allowed the engine to be placed at a higher X dimension.

The term x is the crankshaft to the bottom of the boat. Propshaft centerline is the measurement from the center of the prop to the bottom of the boat. Mine used to be 8" deep now it is 5".