I am a level 8 skier ski on Lange Fluid 120s (90 days/ four years old). My shell fit shows that I have 5/8" space behind my heel and prob 2 mm laterally at my forefoot. The boots have always felt great warm but in the last two years I have noticed that I need to tighten the buckles one more notch and now my feet get a little cold. Also, after a few hours my heel slips a little. None of these problems ever happened a few years ago. Last year I upgraded my 10 year old hard plastic footbeds to new Superfeet Vacuum fitted footbeds (unloaded, I am a pronator). The footbeds helped my performance a lot and these other problems a little bit. I have interpreted these observations that new liners might help with performance, and warmth.
I went to a shop that sells the Fisher Vacuum boots and their fitter seemed competent. He tried me in what I think was the Intuition Luxury Liner (It had a tongue and was 9 mm thick). It felt very loose compared with my stock liner. I realize that the Intuition liner will increase in volume with molding but I do not realize how loose is too loose. Note that we also tried the Zipfit. It seemed to fit more snugly but it was still looser than my stock liner.
My real question is how snug should the unmolded liner feel. I hate to waste molding a liner that will never fit well.