Re: Scarpa SL M3 or Asolo TPS 520

With those Asolos, your heelbox is slightly too tight, I used to fit boots for the largest store in Canada and another dealer as well. You "may" be able to modify these with a boot press, but, it is dammed difficult to do this in that part of a boot, REI "should" have a genuine bootfitter who would know.

What can work is to wax the area with Snoseal or other soft wax and then wear pieces of thin plastic "strapping" aka adhesive tape OR large plastic bandaids on your heels. I do this with all new boots and it saves a lot of misery from hotspots and blisters. Can't hurt to try.