If you go to the APR website, they have some good tech info on there for all of their wings that should help you out. The GTM uses the GTC-300 model and we normally set it so that the center section of the wing is level.
I used the factory carbon wing but with our own mounts, so can't answer your question.
But, I can tell you we put in too much wing, drive it and then back out some wing until the high speed push is gone (or acceptable - I don't mind a bit).
IMHO, you don't need to know the actual angle of attack. You do need to have a way to measure changes and position so you can set/reset as needed. We simply measure off the end plates - so it's not angle of wing, but it is simple and repeatable. Either of these work great: