FWIW, I have been given to understand that the average temperature increase in the air flowing through a typical aircooled aircraft engine system is not very high, actually. If that is true (I've heard numbers as low as 3-6 degrees), I would not expect there to be much difference in oil cooler performance in one with an inlet directly in line with the cylinder head and one that was not.
In an RV or Rocket, because of the speeds we fly, I would expect high flow rates and only modest heat transfer per unit of air. Heat transfer per unit time, may well be another matter. Someone fill me in, please, if I'm not understanding this correctly. If what I've heard is correct, it shouldn't matter so much where your inlet is located since air pressure throughout the upper cowling will equalize. The size of your inlet may well matter more than it's exact location. There has been a lot of evidence and "testimony" on these pages about using 4" SCEET inlet hose (for example) in lieu of 3" SCAT if you're not going to mount directly to the aft baffle itself, which many have recommended against but (as usual), others swear by!
Regards,
Lee...