I have the opposite problem- cannot get them small enough and have to saw off part of the bar. Crampons are designed for a stiff soled boot. You may have to look into getting different crampons. When I really needed crampons, I also really needed a stiff soled boot. Do you really need crampons? There are other traction devises out there (although I have not used them). Any soft soled boot that bends a lot will put quite a bit of stress on the crampon and when the bar is fully extended, I would worry about breakage. Go to a good climbing store and see what they say.