Best way to get speed

Ive been shooting bbs almost exclusively. Im working on getting comfortable at 15M My band question is. Ok I know I dont want to overpower and get slap,,, but has anybody ever worked out whether a thin ,say .40 say 3/4 x1/2 is faster ,,, or if a .60 5/16 x 1/4 is . I want to try to find a formula for maximum speed at my short draw. I know short draw is not going to be as fast as a longer one, but it honestly is the only way I enjoy shooting. I guess Im asking is wide and thin, or narrow and thick faster .

I made a super light pouch last night , out of a one layer of a magnetic bb band , and cut shorter. I would guess this gives more fps owing to the lightness. Ive just been using the cheapo 45x12 pouches. just musing, to me its fun to try to figure this out.

I cut some shiper .60 5/16x 1/4 w 6" active, seems to shoot hard , but I have no chrony, so will give it the can paper penetration test tonight. I have long arms , so even my short draw isnt tiny ,. any ideas ,are quite welcome thanks