I have the same problem with the strap showing a lot on the ankle strap. I thought of maybe just buying Large/ Ex.Lrg straps only. But some people reassured me my Med/Large on my 10.5 foot should be fine with the shrinkage tech I got in the boot. I know how you feel we are at that awkward in between size.
Have you pulled your heelcup out to 2 (furthest setting) yet?