When you are dealing with a relatively narrow hoof and you are using the Fury boot, you may end up in the situation that you select a shell for the current width, and you will need to full length extension of the boot.
Looking at the back of the boot, you can see the shell curves inwards. Depending on the state of the hoof, this part may or may not follow the hoof nicely. There can be the situation that this part pushed too hard against the hoof. The solution is to simply cut it off.
See the photo below on the left where the shell is marked with a black marker pen. For this hoof, here the boot curves in too much. The photo on the right shows the hoof in the boot with this part cut off.
This is a simple solution to ensure no unnecessary pressure from the boot to the heel exists.