The side louvres were "out" until 2004/5 when the Roadster S1 had the air intake right up against the nearside louvres. This was given as the reason that the side louvres were flipped.
Somewhere on You Tube is a clip where somebody covered a Morgan bonnet with tufts to check the airflow, and what that shows is that the air around the side louvres is very messy and turbulent. It also showed that there is a high pressure zone in front of the screen which forces air down into the heater intake through the back four top louvres. So the optimum place to get air into the engine is where the heater box is located.
However, when stationary the air will naturally rise through the top louvres, and when stuck in traffic you can see the haze rising.
