In "Tune to Win" Smith addresses heat exchangers, duct components, and design.
My original design had the radiator tipped back. This necessitated a long roof and short bottom for the duct tract. This configuration dictates more roof than floor to act on. The roof of my duct was a piece of aluminum screwed into the inside roof of the nose. With the radiator tipped back there is some component of force acting up. Assuming the air is attached at speed, it should be very fast across the top of the nose with very low pressure. Though the force should equalize it is not acting on the same surface area.
The component of force acting up with the reduced pressure over the nose can cause lift. We are not talking about street speeds - my interest is in speed in excess of 130.
Please consider this - The engine compartment on a vehicle is a duct. Why do racers constantly try to relieve compartment pressure? 1) drag, 2) lift. The top of the duct is the hood and the road is the floor. The floor is immovable, but the ceiling( hood) is attached to the floor with springs and they will give. That give will take weight off of the front tires.
From my study I decided to see if I could tip the rad forward. The area of the 2.5" cored rad in my FIA @ 902 in^2. I found the rad dimensions for a GT40 MK1. They ran a 3: core at 956 in^2 of cooling surface. I taped together a card board box 14 X 25.75 X 3 (913 in^2) and configured it as cross flow. The box fits in the nose of the FIA tipped forward with a very short intake ceiling and a very long intake floor with the floor attached to the top of the frame rails.
In "Race Car Aerodyanamics" Katz shows 4 configurations of internal ducting. A vertical rad has the highest coefficient of velocity to the face, but also the highest drag. A forward tipped rad with vertical exhaust was quite low in drag, but also still high in velocity.
Here is an interesting Engineering Study on natural convection and the angle of a radiator. It was found that between 30-45 degrees the heat exchanger was more efficient because of the geometric relation of the fins to the air stream. Notice the angle of tip in the Red Bull car. Classes that can't run fans use this to their advantage. Conclusion Below.
Here is a very interesting discussion of radiator angle with respect to F1
Radiator angle and aero balance - Forum - F1technical.net
Your diagram is mis-leading with respect to air flow. With the rad tipped back, what do you expect is happening to the air on the exit side at the bottom, middle, and top, knowing the air exiting the bottom has to pass the top of the rad?
I believe Ken Miles knew what he was trying to accomplish and it was replicated in the 390, 427 Flip, Daytona, and GT40 and countless Sport Racers since at least the mid 60's.
I am concerned about your intake feed. In Tune to Win" Smith discusses trying to pull cold air from down low. The air temperature at tarmac can be 20 degrees higher than the surrounding ambient air.
Provided the air is cold, the extra HP could be used to overcome the potential drag built into the system.
chr