[Frank Lee]

Aerohead has mentioned in the distant past about a device to aid boxy things- like semi-trailers- that consists of a quarter round length mounted such that it stands proud of the front surface and flush with the sides/top. It traps a "stagnant" bubble in front while promoting ordered flow past it to the sides/top.

All indications are that these types of "A" pillars are basically doing the same. Of course since they are angled back on the cars it's not so much a stagnant bubble as the bulk of the air mass is going up and over, but I suspect there are "stagnant" or probably more like sliding zones along the fronts inner to the pillars and the flow to the sides is orderly.

That posit makes sense to me as evidenced by the A-pillar wiper parking, which would be aero disaster with A-pillars that are flush to the windshield.