That was interesting. I always wondered why the purchased binding was folded offset like that.
I'm one of those that likes the look of the binding when handsewn to the back.
I cut my strips 2-1/2" wide, seam diagonally, starch & press in half. Then when I sew it, I sew about 5/16" seam (between 1/4 & 3/8). It's the perfect width when turned to the back. I usually use Warm & Natural batting, so take that thickness into account when trying other battings. It was trial and error for me to come up with that seam allowance. It works great for me. :)