Thinner is faster?

I have heard some people say that thinner elastic shoots faster (thinner=faster retraction speed). This is contrary to my experience.
Why is this? Is it that thinner is faster with only very light ammo?

Lightest I have shot with is 3/8 steel

Or is it that it just shoots faster for the draw weight.

So not really faster at all just easier to pull.
I saw a Simple shot video demonstrating this. Thicker elastic shot a bit faster but at the cost of alot of extra draw weight.

Or maybe cutting thin bands wider then more narrow thicker bands can get better speeds....but that just comes down to draw weight again.

Obviously hunting purposed bands are always thicker then target shooting bands so unless it's the light ammo thing I can't see how thinner bands could be faster???