Michael...believe Campy's overall rim diameter which makes tire mounting difficult is intentional. The design priority is clearly skewed in favor of retaining the tire bead/sidewall under extreme pressure and temp with the consequence of difficult mounting. My educated guess is Campy's overall wheel diameter tolerance is very tight...less than 1mm or .040". Why? Because of how they process the wheels...they start with an oversized roll extruded V section and butt weld it into a closed rim. They then machine the wheels for a pristine and planar braking surface and easily control the O.D. of the wheel for runnout and size by finish machining which is critical to tire retention from a liability standpoint and of course affects tire mounting which are two competing factors of design...tire retention always getting the nod from a liablity standpoint as it should be...and why they do what they do.
George