I saw a Sharon Schamber video where she showed using a light spray of starch while loading the backing on the frame. Put it on the front bar, roll it onto the front bar, attach it to the back bar, then when rolling it to the back spray each section with starch.
I tried it on the latest one and man, it did good. I didn't iron the backing at all after washing and drying so it had those little tiny wrinkles all over. I sprayed it and just watched all the wrinkles magically disappear and it was tight and smooth.