Oh, one more thing, as the angle of attack increases, the geometry of the cooling air exits increases the exit area. Its like having automatic cowl flaps, or money for nothing and chicks for free. 
Please expand on this statement/concept 
Lets start with this:
Specifically,
Fg. 1
This simple diagram provides a lot of insight for cowl flaps, exits flanges (lips) and general exit design.
Another inference I gleaned from this is that extending the exit ducting aft of the firewall is nonproductive.
The sonex FW is angled at 30 degrees to the horizontal axis . In level flight, the airflow is very close to being parallel to the horizontal axis. THe exit opening is 2 inches deep (or tall) and measured perpendicular to the horizontal axis is 10 inches. As the aoa increases, to say 30 degrees, the airflow becomes perpendicular to the firewall ( the hypotenuse) the length becomes roughly 12 inches.
So, like I said, “Money for nothing and chicks for free”.
BTW, the NASA study is available online as a PDF for free.
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