Default Case-Mate Naked Tough

Just picked up this case for my Moto X with a carbon fiber back - fits great. the one thing I noticed is that there are like 2-4 :spots" on the back of the clear case where it touches the device and makes like a little swirl mark. I'm assuming that all cases that fit right do this but, generally, cases with a black or solid colored back simply aren't visible.

Just wondering why the clear case would touch some areas and not others?