In this image in the lower vortex generators a couple inward rotating vortices are depicted at the trailing end of the VGs.
These 2 vortices then cross themselves to form a bigger car length vortex as depicted in the crossing lines.
This larger vortex works pretty much like a side skirt preventing outer air from getting into the venturi tunnels and diffusers, also reducing diffuser flow separation.
What modifications of improvements to the twin Vortex generator / bargeboard setup enhance this large vortex?
Now the big question is If twin bargeboards are banned what single bargeboard design allows it to function as a dual bargeboard setup or better?
The rewards for answering these questions are getting side-skirts like ground effect downforce levels!