Below similar to the TV show Wheeler Dealer episode with the 1985 Ford Escort RS - Cosworth.
Was this:
VWVortex.com - So who didn't catch the Escort RS Cosworth episode?
Now this:
Wheeler Dealers: S14 E1
That middle wing shown above added 25 lbs of down-force in the wind tunnel, no idea how much drag it added though.
I suspect this works similar to my proposed Porsche 911 Sponge Bob tail.
Now I'm wondering what it would look like with three tails terracing down.
One off the roof line/Targa bar, one as shown in the middle, and a third at the bottom of the deck lip just above the rear tail lights.
Total overkill, but I have lots of business cards that I can cut up and play with.
I would terrace or step them, not stack them as in the Escort RS.