I was always taught to measure each side and put the exact border measurement on each side. That way the quilt will lay flat. You can play a little bit with less then an inch difference but over that amount you will have a little mound of the quilt in the corner when the borders come in tighter than the quilt. I quilted for those who just sewed any length of fabric on the quilt and it was difficult trying to get all that excess fabric to lay flat. But the opposite also occurs and if you try to average too much, your borders will bow into the quilt. So much I learned when quilting for others. You could trim you quilt if you wanted it to be perfect. The blocks are floating enough with a little room to trim without it showing.