First three shots are of cowls on two Extras, the big one is a gasser and the other one is a glow powered Extra with a YS 1.20 FS for power. They are both opened up with a lot of over kill on the bottom. If most of the engines head is sticking out you don't need as much air flow but both of these planes have had different engines installed at some point so the cowls were opened as needed. The yellow Sukhoi I scratch built and for the most part only the head and muffler are sticking out. As set up I was going to fly the plane and see if it needed more air flow and open the cowl as needed. As it was it never over heated due to air flow over the head so the cowl worked out fine. I have another shot of a scratch built Krier Kraft Bipe with a lot of air flow going in like on the Suk but the head was sticking out enough that it never over heated. Looks like you have plenty of out flow but you opened up the front way too much.