I think I finally understand why they fit a C5 application the way they do. An ATS rotor is only 321mm in diameter vs the C6Z at 355mm. The caliper assembly must mount further inboard on the Cadillac knuckle. That comes out to 12.6", some wee rotors for sure. GM was pretty consistent with rotor thickness though. So the different diameter rotor has a longer, lazier arc than the smaller ones, that's why you have to clearance the edges. It's just dumb luck that it all fits the way it does
