If you play a CF with no appearances at the corners, you will lose very little from his CF performance (especially in LF); arm will hurt you in RF.
BUT...if the same guy gets an insignificant number of appearances with no chances or few chances, he will have a wildly distorted performance in the corners. I did ok with Posednik in RF for part of my games in RT last year, but didn't dare put im in left.
It's an anomalie that should somehow be corrected...though probably can't be a high priority.

Dave N