Here's what you ask for, but I wouldn't put too much stock in it:
Mainly because it shows an angle and flat plate, whereas I think the shape should be the top half of an exponential horn, IOW curved side walls and a curved roof. The Elipse has a flat plate and fanned fences. Here's one I like:
It has curved sides and no fences. Notice that it starts immediately inside the tire and curves out approximately the tread width. That right there will block turbulence from the wheelwell from getting under the car and throw it out into the ambient flow.
Then the expanding section slows and pressurizes the air (I think... aerohead?) to raise the base pressure.
As for the fastback, I think the prettiest car ever is the Shelby Daytona coupe. Here's the electric version by Renovo:
http://jalopnik.com/the-renovo-coupe-is-an-electric-shelby-with-1-000-lb-ft-1621969757