The LA I sometime use for my larger quilts say my borders are always flat and even. I don't measure them, I sew and cut off to fit. I cut crossgrain not lengthwise. If I have a floppy border I use the tuck the excess under the seam as I posted earlier. I don't know who or when someone decided the border had to be measured made to fit the measurement through the middle of the quilt. I'm sure it works on paper and be manipulated to fit to be exact but I don't have the patience to mess with all that when it's not necessary.