[aerohead]

I don't think so.
The windshield header is already submerged within a favorable pressure gradient, as far back as the roof apex.
And, as far as the CFD suggesting that flow is separated there, I don't believe that to be the case.
It's just a very strong suction peak, and very strong pressure spike, which lowers the ability of the boundary-layer, rear of the roof apex, to withstand the adverse pressure gradient of the fast falling roofline, triggering the flow separation we see in Volkswagen's wind tunnel photos.
Hucho wrote a comprehensive explanation of how beneficial it is to 'soften' that area of the body, with respect to its affect on flow adhesion downstream.
Dr.-Ing. Eberhardt, who designed ROVOMOBIL was no doubt aware of what his 48.5-degree windshield slant could do.
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The rain, 'over-shooting' the header is more about the inertia/momentum of denser water, compared to air. The air would have no trouble rounding that intersection.