as has been stated, very difficult to assess your assessment via the internet, however, the guys have hit the high points.
the challenge is to help you have a fighting chance at improving your skiing, without compromising your joint spacing and putting you at risk of injury.
as mentioned, the places to look are at the STJ (sub talar joint ) effected most directly in the ski boot by the angle of the bootboard side to side at the rear foot or forefoot, as well as the same angles in the footbed which rest on top of the bootboard. so if all is good there, you move on up the chain to the cuff of the boot, at the cuff, we want to see that the shell is not putting additional stress on the STJ, this is accomplished by centering the cuff to the leg as it comes off the bootboard/footbed. the next joint to get stacked over the feet is the knee, this relates most strongly to the sole angle of the boot. most boot guys that have been around the block a few times, get a little funny feeling when they see canting indications that cross over the 3 degree line. that is a lot of cant. in some cases, just moving the skier closer to the target in the correct direction, will give a huge improvement on snow. the hesitation that the bootfitters have expressed at going past 3 degrees on the sole is related to the closing and opening of joint space at the knee. there can be consequences for the action of changing too dramatically the relationship of the joint spacing at the knee.
there is no universal training for bootfitters, so make sure that you have confidence in the assessment of your fitter and the resulting changes that he proposes.