I used FM to PM on a medium, with XTR M9000 brakes, and the brake actually touched the seat stay. I had to grind the brake bolt to clear on the Medium FM199. Not something I was happy with. I was getting terrible harmonics with the rear brake set up and in the end, I had to install the caliper flat mounted with a 140mm rotor. I tried many many combos of rotors, calipers and cleaning and could never get the harmonic squawking to go a way with a 160mm rear setup.