A thread from 2015 documented Morelli's FIAT research car.
EcoModder Forum > EcoModding > Aerodynamics > Morelli's 'Fluid Tail'
This had every trick in the book.
Oval terminus
Active aero evacuated wheel wake
Box cavity/separation edge
Perforated [not even sure what this is]
Here's another picture from the same thread:
https://ecomodder.com/forum/showthre...tml#post503632
It's got speed holes. Maybe those would help with the local authorities.