Was reading through randomly after 30+ pgs on this thread today...
The Bullet Project - Wikipedia, the free encyclopedia
According to the Aerodynamics section, they refer an advantage utilizing Compression Lift
And Here:
Compression lift - Wikipedia, the free encyclopedia
I think that with whats being stated, with the XB-70's(1960's) fins "decreased the induced drag about 30%". And the fins having a greater effect at supersonic speeds as of the LSR car, is happening with these fin'd race cars. While at moderate speeds, they must assist in some degree.
The first car 1964 LM64, not matching the template and its shorter length, its steep slope may be creating a larger "wake", and has long fins needed to catch the wake with its high "attack" angle, could be Forcing this phenomenon to happen at a greater rate with its slower specified speeds to further assist in Stabilization(this is a race car after all) and producing just enough downforce, at the same time reducing drag. (All this Aero evolution around the same 1950-60's era)
Then moving to the more template based 1967 Peugeot 66C with its more Upright fins, then to the newer Matra640 requiring further less "force" to enduce this "compression lift/stabilization" with even shorter fins, with again less "attack" angle.
(Like Pitch control of an F-117 Nighthawk)
...Reminds me of the EVO Lancer, with their ultra sciency vortex generators and spoiler to produce attached flow, massive amounts of downforce and lowering the Cd at the same time...