[aerohead]

I couldn't get the audio portion,but I think I'm okay with what they presented in the context of the 1/18-scale models they depicted.
Any separation which occurs 'over' any portion of the body will induce lift,which is induced drag,which increases overall drag.
A carefully 'tuned' airfoil of just the right size,and angle of attack,can mitigate the lift do to separation,reduce the overall drag,which would win the drag race if long enough.
It would be on a case-specific basis,so whatever you saw on a Carrera,you wouldn't want to put on a Lancer,or anything else.
PS Merely lofting the roof-line up to the ideal pathway would kill the lift right there.