All my FM199-B builds had extremely close clearance between the chain and chainstay. The chainstay always exhibited signs of rubbing (small scratches and small groves). I used properly installed boost spaced Race face Next SL cranks Gen3 and 4, and Shimano XT M8000 Cranks boost spaced. All rubbed. On the race face, I had to flip the cinch chain ring inside out (backwards) to get proper clearance. Not something I was happy with, design wise.