I too used to make my binding 2.5 but it left a little space and I didn't care for that. So I started cutting them to 2.25 and it still left just a little space so now I sew it on at 3/8 instead of 1/4. Seems to fit just right for me now.
I normally cut my binding at the time I start putting my last border on so I know I have it when I need it. Some of my UFO's had the old size of 2.5 for the binding but I didn't cut it down to 2.25 as it was just too much trouble for me at the time.