OK I think I will leave the bottom clearance at 4".
I thought that the idea was to keep as little air from going under the car.
I was wrong this aero stuff is killing me.LOL
The only time I will need down-force would be at the track and the hill climb.
For the most part it will be used for hopefully 1000 mile road trips across the great western United States. I will be mostly on the Interstate Freeway system but you never know when I have to stop to get food etc. what the roads will be like.
So today I will see what a 15 degree drop roof angle will get me for the bottom rear piece.