Depending on the scoop, it may suffer from packing. Too much air enters a space and has nowhere to go. The scoop basically can't accept any more air. Cutting a hole in the rear allows air to flow through. It's a balancing act.
Is there any proven math for this?
this is purely speculation here BUT
Thinking a little deeper from my statement above 1.5" tall X 12" wide X2 scoops= area of 36"....../ by 8= 4.5 So 4.5 5/8" holes in the back!?!
