Eugene's engine is liquid cooled, so there's not much need to guide a lot of air through the heads and cylinders (as we'd have to do with a Lycoming, VW, etc). The vast majority of the heat will get into the cooling air via the radiators (for oil and coolant) at the front of his nacelle.
Well of course it is! Duh! I knew that but for some reason it simply didn't register with me. I don't know what I was thinking...