I have '12 Vitas wearing 9's (fairly high profile '09 32 Lashed) on Mediums.
To your original post even though you already have Burton's help, I will agree with your difficulties just so you realize you are in company here. I really like these bindings, but between the solid plastic design (which I love but makes the heel loop not move) and the reflex in the disc, there really is hardly any way to make this adjustment.
To their credit I spent some time on the phone with Burton (none on hold) and they sent me out a bag with like 8 discs for me to try(indeed one of those sets did work better, basically you have ones where the holes are parallel to the reflex bend, or perpendicular to it).
GL with the mediums, but perhaps you would do well with a different set of discs.