I tested 3 angles and this last angle is 6.3 degrees more than the last. Angles were with 3 degrees steps:
Like that it is quick and easy to test various angles. When you tilt the spoiler more it is wise to cut the exess material off from the sides. I just measured the current angle it is about 11.6 degrees so about the max is that 17. I might have to do more tests even higher angles. I will also try to get better visibility to roof tufts.
Here is a video of the first setup:
I did ABA test on this first angle and got results that it saved about 4.15% on average to both directions. Better test need to be made.