I think that biggest reason why we need more fan, is that air can't find its way to out.
Old VW beatle was dense like mordern cars. (Beatle could float on the water pretty long time) Heater couldn't blow the air from back of the car to cabin. It was needed to add also air outlet to back of the car. I think that same thing would help with modern cars. Easy way to test this theory is to open window littlebit and you get much bigger flow.
Beatle also needet thermal insulation to inflowline to get cabin warmer.
I think that you can't get measureable gains to FE by changing the intake place. Outlet place is more importan. Same thing with cd: You can get more gains from back off the car than from front.
This is just my point of wiev.
