Ive answered this one a few times. Its Potentiometers! We hate Pots pots pots! Without taking up more space, please see the thread "Calibrating Distressors". Its the same problem - pots dont ever match each other exactly. There are certain places where they do match, and certain places where they dont!
This is the reason on mastering rigs, lots of companies go to the verrrrry expensive switched attenuators - Pot manufacturers generally SUCK <laughing>. For your information, switched attenuators are typically 10 - 20 times more expensive than pots, each attenuator often costing more than $60 each! We may offer them in units as upgrades someday... but dont quote me on that!
We'd be glad to look your unit over for free but, one of the reasons we use the high resolution knobs is to allow accurate notes of settings. I suspect your pots meet our spec which is that they will match within about 2-3 small tics - one tic = 1/10th a number. We'll be glad to double check anything for you, free of charge, as always.