"Pressure cowling" is a design that blocks the airflow that would go through the cowling but not near what needs to be cooled, the cylinder fins etc. The baffling fills what would have been open areas. The baffling comes right up to the cylinders but stops short, leaving space near and through the fins for the air to flow. THEN the negative pressure area behind the engine that is created by the low pressure zones behind the cowl flaps etc attracts the air that's coming into the front of the cowl. That air has only one way to get to the negative pressure, and that's very close by the hot spots.

There's a positive pressure in front, that wouldn't do spit if allowed to blast through the cowling. Hot air is harder to move, and the hot air around the hot engine parts would simply give the cooler air something to avoid and to go around.

There's a negative pressure behind. And there are some paths from the front, right by the hot engine parts that need cooling.

Next time you have the opportunity, walk up to the front of a P47, Corsair, Hellcat, T-6, or any big engined bird and look into that big hole in the cowling. Most of it is blocked off. Now step back just behind the cowl flaps. When some of them are open, you can see daylight inside that cowl. Not much. But lots of air can make it through there when that big old bird is thunderin' along.