I use 21/2" width and a 3/8" seam. When I used the 1/4" seam it was always empty at the fold, now it is all full. I did think of going to 21/4 but decided the 3/8" seam would be better. How was the 31/2" put on, you've got me thinking it must be very wobbly, loose and no support to the edge.