frostbite,
sorry i have not been around recently...skiing and working
it sounds very much as you say that the boots are too big, or at least have too much volume in them, blisters are caused by movement rather than pressure so we can assume that the boot is not too tight in the area where the blister occurs the first approach [asuming a new boot is not the answer] is to put a heel gripper into the boot, this can come in two forms, either a plastic frame which goes around the back of the liner or a wrap made of either foam or leather, i prefer leather as it does not compress as much nd therfore lasts longer, layers of 2mm leather can be added together if required...... alternatives could be an aftermarket liner such as intuition or to take up a bit of volume zip fit...but this is only a viable option if the boot is the correct size
there is lots of talk about how much space there should be behind your heel in the shell of the boot with the liner out and toes just brushing the end....... a lot of it depends on your tolerence, the quality of the footbed, and the shape of your foot....if your toe shape is a very accurate match to the shell shape at the front then you can get a way with a much smaller boot...but as a rule
8-10mm world cup fit, up to 15mm performance fit up to 20mm comfort fit, up to 25mm extreme comfort [exceptional circumstances] any more ...plant pot
hope this helps a bit, if you need any more info feel free to ask, if a don't come back to you quickly, ping me a PM and i will respond....i just don't get on here that often at this time of year
