Maybe it is me, but I am thinking if you wanted to reverse the sashing to the back, wouldn't you just reverse the sizing of the bocks? Maybe not since the drag on the backing would occur while the flip sewing happened. I would say then, just make the front and backing the same size, cut the backing to the smaller size when you are finished, then meet the fronts together and sew the seam,and hem the way they say to the back. Am I right? I am dizzy just typing this. My abstract reasoning is really bad, girls. LoL!