I dont remember on which bikes i did it, but i 3d printed some thin (c.1mm) half moon-ish spacers to go above the C ring (it was a C ring with 1 position knob sticking out) so that the 1st plastic thing sitting on top of the tube wouldn't rub on the frame. I had to do that using bars i didn't buy from whomever sold me the frame, but my point is, if that plastic / metal rubs on the frame because the C ring isn't high enough / the bearing isn't tall enough, you can get away with a basic 3d printed spacer (i did 2-3 prototypes, the whole thing probably took me 2h across design, iterating and printing), that avoids having to sand / machine / lathe the bit that sits on top of the frame.
I also used spacers on the drive side of cranksets, BB tools (tightening & extraction), saddle bottle cage mount, garmin mount for aerobars... It's a great resource to have.