Mike,
Sorry for the delay in getting that chapter from the book scanned in, my scanner for some reason is being a bit of a pia. I bring the book into work next week and scan it in there, I can also make it as a .pdf that will make the file size a lot smaller. I think what Da was saying that the actual distance you should have for the spacing from the engine to the inside of the cowl is about 1/32 of an inch max, the thickness of a t pin. You want the air to flow around the engine, not through the cowl, and as he mentioned how it leaves the airplane as important as how it get into it. Also the shape must blend the airflow back around the fuse so the back of the cowl is as important as the front.