Is there a problem with cutting air exits in the firewall and letting the air flow through the fuse?
What's going on is you are building HI PRESSURE Inside the cowl. So NO real air FLOW to speak of. Take the cowl off and the air flows from a radius behind the engine.
Think of it this way.. Turn on a Hose and block the end. You will have high pressure in the hose but no flow. You need the out side LO pressure on the other side of the hose end to have flow. Air is the same way, it acts like a fluid.