My new Sidi's, despite being 1/2 size smaller, are quite a bit wider in the heel (my old ones were Genius 5's, new Sidi's are Genius 5.5's). My heel moves up and down during the pedal stroke. Anyone know of a trick to tighten it down inside the pocket? I tried some ski bootfitters foam, but it won't stick to the mesh inner lining. My foot is a pretty standard C-width, but a bit narrower than average in the heel.