[kach22i]

I would not call the top foil on the white car a "vortex generator".

I would call the tiny shark fins "vortex generators", and you did not post a photo of those.

I agree that if a garnish/device redirects air somehow to a second device intended to increase drag and down-force, that this second garnish/device will operate more effectively. I have this same exact situation with my roof wing and rear spoiler, see roof wing in my signature below.