Z3 coupe clearly is one of the cars that this rule targets for roof height +4", while the Z3 roadster with hardtop is obviously 6" below the roof peak. Now I was wondering, and Greg since you're addressing this subject, what's the height of the roof of a car without a roof? (Maybe, I should start arguing for the number of angles that can fit on the head of a pin *) So would it be 4" above the trunk lid, 6" below the top of the windshield, or 6" below the top of the roll bar?

*(this is a contentious and sometimes deadly debate amoung medieval ecleastical types)