Dick, the air velocity from the prop blast, and the cooling effect thereof, is the same 3" from the back of the prop, as it is 12" back. Not sure how you could say the cyl heads somehow don't "see" the big ol' fan in front of it. I have had my bare hands very near the cyl heads with the engine running (for taking RPM and temp readings) and, on a cold day, the cooling effect often exceeds what I can bear.

There might be some near field effect with a large cowl that may reduce the effective thrust the prop generates, but air flow over the fins WILL cool them. That's what the fins on a air-cooled engine are there for.