Svend....with regards to the overall shell fit..for the foot, contact should feel equal around the foot....actually I like to do this with without a sock on to get better feel points through out the boot. This includes heel, the last area, side of foot, 6th toe area,...starting with a boot that's 95% there is a big plus. Sometimes mod's in the 6th toe or ankle bone areas may be required but essential fit areas I think are the forefoot and heel. Also look for even spacing in the upper cuff when you stand in the shell. Most top end boots, the cuff can be tipped one way or the other but it's helpful if the shape of your lower leg fits the shell with even spacing.
The race performance or high performance boots all have tighter tolerance than lower end boots. I've found that if the heel fits in the pocket well, the Achilles area fits too but keep in mind that spacing of the entire lower leg should be even all around the upper cuff.
Finally, I think it's got to be done without the liner for the best fit. The liner can hide a ton of issues. Having someone that has an eye of what to look for, a good boot fitter is extremely helpful. Standing in the shell with the foot bed in, in your ski stance, arms at the pole carry position, looking straight ahead...."be one with the force Luke"...listen to what your feet are telling ya...!

best, g