Bruce buddy, I can't help but wonder why you would go flat on the back panel? I know you prolly want to see out the back, but in my mind, the Honda is pretty darn good to begin with. If you want to improve on what Honda has done you are going to have to sacrifice something and in this case, it is rear visibility.
I don't see how a flat back is going to smoothly transition the air down the back of the car. Also my intuition is telling me your sides being higher than the flat back are creating a vortex generation situation... as in the big bad wing tip type, where you have vastly different pressure areas in contact with each other....sucking the life out of your mod, and, the FUEL from your
TANK!!!
but I digress.
I think you either need to shorten the sides so they don't stick up above the flat tail, or, to optimize the mod, put the top of the kamm back at the top of the rear window and bring it down to a inch or 2 higher than it is now at the back and keep your sides the same as they are.
Sorry to be so lazy here, but I'm just going to post what I want to do with my 5th gen 04 sedan, pretty close to the same idea. I think you'll still have some good views out the back under the rear edge of the Kamm.
You're doing great to just be doing something, keep it going.
Charlie