Sounds like your fitter did the opposite of my fitter. I also have Gold Medallions, and also have one foot that is longer than the other. In my case, one boot is ever so slightly too big and I solve the problem by use a heel liner in the right boot, which fills up enough space for it not to slip. I do sometimes have to re-lace that boot to make it tighter at the ankle, but this isn't a huge issue given my level and the amount I skate.
Obviously that doesn't answer your question, but interesting how different fitters approach things.