Cd 0.21 Ford Fusion 999 hydrogen LSR spoiler
 

I ran across this CAR and DRIVER image, which may be as close as we'll ever get to a true-length rendering of this car.
None of the other photographs appeared to represent the actual length of the 'Bonneville' spoiler, and how it relaxes the apparent roof-to-trailing edge length and angle.
https://www.caranddriver.com/photos/...lery/?slide=12

https://hips.hearstapps.com/hmg-prod...-s-986x603.jpg

with the [?resize=980:*] removed

One can see the top of the side plate, is the plane at about the bottom of the 999 lettering?

plane of the shelf extension
 

You can just make out a line of rivets in the green of the capping plate. I'm not sure about up above.
There's a photograph taken from above the car and it appears that the extension drops a bit as it progresses rearwards, as an extension of the trunklid ( boot ).
I printed an 11" X 17" color copy for the light table and drafting instruments.
Real people will scan it into their software package.
HOT ROD Magazine's Project Red Hat, LSR Camaro, Cd 0.20, showed a perfect template match off the backlight onto the spoiler top.;)

I just have a 4" brass caliper that I can hold up to the screen. :(

One of these days, I'd like to make a drag spoiler for the Prius. If done right, it could potentially reduce drag AND lift.

screen
 

1) sticking 3M POST ITs to the screen will lock in the virtual angle.
2) Additional POST ITs will establish the ground plane beneath the wheels of the car.
3) Then a 50-cent protractor can be used to 'read' the new slope angle, referenced against the ground plane.
4) With all my photo-enlargements at identical scale to my templates, the light table allows direct overlay 'X-ray' comparisons.
5) 'Blueprints' are the way to go, but we may never see an actual technical image for this car.

Prius
 

https://www.caranddriver.com/feature...mparison-test/If you can locate CAR and DRIVER's ' DRAG QUEENS' article, you might find lift data they measured on their Prius at the A2 Wind Tunnel. My foggy memory suggests that Prius had one of the lowest rear lift measured. You'd want to check.
1) The 2014 Prius EPA test weight is 3480- lbs.
2) It's rear lift at 70-mph = 17-lbs, same as Tesla Model S. The Nissan Leaf had the lowest rear lift.
here's a link:

Interesting article. The data look promising. But I still think there's room for improvement.

Fill me in, is rear lift good or bad for mpg?

In theory neutral would be best. In practice it would depend on which end has the drive wheels.

Fuller's original Dymaxion (reverse trike) design was a tail-dragger that lifted the third wheel and drove and steered with fronts. Jocko Johnson stole the idea for his Triple Nickel speed record car, but he didn't live long enough ti instantiate it.

I can't think of any other counterexamples.