I have the same issue in that the right calf tends to cramp. This has lessened over the past 3 years which indicates it is a leg strength issue. What helped was to move the cleats as far back as possible. These are Shimano mountain two hole cleats. Using a round file, I elongated the holes as much as possible, 10 mm and also files the metal plate in the shoe so that it would move back enough to line up with the cleat bolts. This helped quite a bit and as legs have gotten stronger the problem has all but vanished. I've also begun, just in the last few months, doing calf strenthening exercises. Cycling is repetitious so if anything physically is even a small amount off in you or your setup, you are going to feel it eventually.