[aerohead]

I finally located a photograph for wind tunnel smoke-flow imaging of the 2020 NISSAN 370-Z ( I'd originally found it online ).
Three smoke filaments are presented.
The second-lowest makes contact with the boundary-layer on the windshield, over the top of the roof, an then separates immediately beyond the roof apex.
The 370 is 1,315mm high, and based upon the 'daylight' between the trailing edge of the upper body, and the local streamline, there's a 82mm separation gap.
A first-approximation solution for reattachment would be a shallow, upswept rear spoiler, with its tearing edge just touching the bottom of that streamline.
Dr. Hermann Burst might have recommended lofting the entire rear contour up to this imaginary line connecting the span.