Full scale planes use both techniques to reduce cooling airflow. Many planes have cockpit adjustable cowl flaps that restrict the outward airflow to control engine temperatures. Others use airflow restrictors in cowl inlet openings with some only being installed during winter operation. Most full scale planes that use the flat opposed engines restrict airflow into the cowl to less than the full size cowl opening. Find a small airport and go look at something like a Cessna, Decathlon, or even a Pitts, etc. and you will see what I mean. Its part of the cowl baffles on the full scale.

For your Pitts, I believe I would restrict the intake a bit. A side benefit, it would even make your cowl air inlet openings more scale.