I usually start this the same way every time. cut off wheel on the angle grinder and cut vertical strips out of the piece you want to remove. then start hitting at a few different angles. eventually, most of the pieces will start to fall off. Then, swap over to your flap disc and start smoothing. When the bike is torn down for paint, I'll really go fter this top tree with a sanding wheel, buffing wheel and then polish and make sure all surfaces are even.