Ok, let me see if I got this right.
This type of angle diference is (I dare say) rougly calculated for a speed well bellow cruise, where lift issues are more critical, and so turning the a/c more stable due to a constant pressure on the back of the frame against a slightly forward CG downforce. That would explain why at high speed (cruise) the a/c body is about 2 deg. nose up. Seems logical enough to me but is this right?
GD&L