Wish, I could be more helpful, but I've exhausted my experience. I sometimes get a faint wrinkle on larger squares (perhaps something with how the icing dries in the corners?). I've experimented with using a royal icing mix that has more stabilizers in it on these very big cookies (over 5 inches) and then drying at a very hot, dry room temperature, and that helps. I no longer dehydrate on cookies over about 4 inches, as I am getting cracks and waves, especially on large angular cookies. I realize this comment sort of contradicts my earlier one, but I have gained more experience on larger cookies with a new dehydrator since then. Even so, the results are not always predictable.