I'm having a hard time getting a front derailer (FD-6500 31.8 clamp style) adjusted where it works well in the small, trim, and large ring positions. I can't figure it out (and I've setup many front derailers perfectly) so I take my calipers and measure the distance between the plates and it measures about 11mm. I measure the another FD-6500 (braze-on style) on my other bike and it measures 14mm. I measure a 105 FD-5500 and it measures ~14mm also. Could the 11mm derailer be bent without obvious signs of damage or bentness?
Can it be fixed?

Thanks,
Henry