aero testing stuff, really good IMHO. WTMFT ( way too much free time)*
I treat auto aero with the sq in. of involvement theory. The less square in. of parts that the air hits, the better.
Along that road; reducing piece count under the car is a major area for improvement . IMHO.
So yes, I think that a belly pan , deflecting the air off of ugly parts will go faster.
Keeping air from under the car turns out to be the best .
Some control over the car will show some improvement. The rules play the big part here. reality plays a big part. Will you have any major speed increase ? At long , high gear pull tracks, MAYBE. maybe not.
As far as your bumper goes. if it splits the air above it and under it It will go slower. If it is the splitter and very close top the ground, than maybe.
The flat front with a small splitter, very close to the ground , directing air around the nose and above the car will be the best,IMHO.
Taking the rules to the limit;. you should need a plumb bob as you go around the nose panel/airdam/splitter .
Take a look under the modern VW TDI or some other high fuel MPG car. If the crap did not work, they would not go thru the hassle of putting it on there.
Back to the rules tho, I still have the front end of the HP tapped up and cant tell if it is legal. I guess that the tape is legal but any screen is not. stupid stuff. IMHO.