Hello Duplo,
I remember you from a thread on adapting an Atomic releasable cuff boot for a heel spur. What is an interesting possibility is that there is a direct correlation to heel pain in ski boots relative to the range of motion or lack thereof in the ankle joint. Low flex ankles will have a tendency to lever the heel off the boot floor therefore "bumping" into the top edge towards the outside of the calcaneous or heel bone. Hyper mobile ankle joints can also bump hard into the heel bones on the back of the shell as the hypermobile ankle can allow for the foot to collapse in the midfoot which could force the heel bone rearward in the deepest flex position of the boot.
From the internet, I cannot assess either the range of motion of your ankle joint or what the situation is that caused heel pain in that boot and no heel pain in other boots that you owned.
Assessing the range of motion in the ankle joint has to be done in a manner that isolates the basic "saddle" joint of the ankle. To isolate the ankle joint the first thing to do is take the body weight off the joint and position the foot/lower leg in a neutral position where a repeatable read can be taken. You can do it low tech by simply using your eyes to see how big a gap between the floor and the 5th metatarsal head you can create. Me personally, I use my pinky finger and or 4th or third finger as my measuring tool for ankle ROM. You could also use a digital angle meter if you are a numbers kinda guy.
Basic premise... Seated position in a chair or bench that will have the femur parallel to the floor when the feet are flat on the floor and the lower leg comes off the feet at 90 degrees, the femur should create a 90 degree angle to the lower leg, and the back should be 90 degrees to the femur at the hips, meaning that your body mass is mainly supported through your ass sitting on the bench or chair and your feet are semi weighted on the floor. Your thighs, shins, and feet should all be parallel and approx hip width apart so there are no diverging or converging angles of right or left side. With out any directional torque of the foot, the fitter would hold your heel bone to the floor as you lift your met heads as high as you can in a direct line towards the knee. In this position you would either measure ( for me with my pinky finger ) directly underneath the 5th met head to see how big or small the range is. Few or no fingers is tight, 2 fingers is normal, and greater than 2 is headed towards hyper.
So normal ROM for humans is 10 to 18 degrees for dorsiflexion. Below 10 degrees is tight and over 18 degrees is hyper. To find the matching net forward lean for the set-up of the skier that you are looking at is simple math of subtracting the ramp angle of the bootboard from the forward lean angle of the boot spoiler. So if the skier has an ankle that is 1 pinky finger that means that their number is going to be below the 10 degrees of a normal ROM ankle. If the boot spoiler is 17 degrees of FL, and the bootboard stock out of the box is 4 degrees, you would subtract the bootboard number, from the FL number and in this example the net number is 13 degrees. The ankle in this example is only one finger, so for this example the ankle has about 8 degrees ROM. How do we get the net FL number to match the action of the ankle joint? We get the net forward lean number to match the ROM of the ankle. So for this boot we cold raise the heel height to make the bootboard ramp angle to be higher ( lets say that we raise it enough to make the ramp angle 7 degrees), and then take off the FL shim that was screw riveted to the spoiler. This will make the boot FL go to 15 degrees. Now subtract 7 from 15 and the net FL angle of the boot is now 8 degrees... Bingo!!! A love match between the ankles ROM and the boot that the ankle is going into.