definitly running along the rails! if you have your seams running top to bottom as you roll your quilt that seam builds and builds extra layers so the center of the quilt is very thick and your sides are baggy, flapping...with each turn of the quilt the center is another 4 layers thick compared to the one layer on the outsides. i try to always load with the seam nice and straight along the bar so when i roll it it is even the full length side to side. no building up and causing wrinkles, uneven areas