It's the difference between a low pressure area and a high pressure area. The front part of a hood is a low pressure area. The cowl area at the base of the windshield is a high pressure area.
Ever notice the NASCAR boys all draw their intake air from the cowl. Now look at the NHRA Pro Stock cars. Where is their hood scoop? It's up in the air stream. If they could reduce drag by getting the same ram air effect from low on the hood they would.
Okay, more proof. Almost all, if not all hoods slope down at the front. If this was a high pressure area hoods would not fly open when a hood latch fails.
Sorry, I did not answer your question did I. No, the test was not done with a sealed ram air system as that was not what was being tested.
Once again, what was found was that the faster you go the more air goes over the hood scoop, not into it. This was verified by the air speed actualy dropping the faster they went, and you could also see it by the ribbons lifting off of the surface of the hood in front of the hood scoop.