Did you sand it down? Did this work? I'm having the same problem. Massive design flaw by Thinkrider...
Maybe that's why they are so cheap, due to the fact that it isn't compatible with all Easton interface cranks.
I tried to remove as much plastic from the outer housing, but at the end I found out it will never fit.
Due to a edge around the Easton interface. The power meter has like 41,8mm edge and my crank arm has a 41,9mm edge, so even when it will not touch the outer housing it will never be flush mounted.
I ordered the cheap aluminium crankset with a second pm and will send the first one back (obviously the untouched one..)
Also changed my BB form 29mm dub to 24mm due to some issue with it, cheap ceramic bearings....
Installed the new crankset yesterday and waiting for better weather for a ride outside.