Masonry directly on the wall generally gives you no clearance to combustibles reduction but it's still clearance to combustiblesSee, I thought that was not allowed.
As in, if you are an inch over your minimum CTC, then adding 1.5" of something like rock (non combustible, but also low R value) on the wall, then you'd be 1/2" below minimum, because the rock could conduct heat to the combustible surface.