RE: Down elev -> ail mix?
Here is some experience with the FOCUS aircraft. Well, let me clarify about the spin entries... I thought about it some more.
Now, before I changed wing incidence, I mixed in some right aileron with low throttle. This kept the wings (and plane) tracking straight in a spin entry (particularly inverted spin entries, since at the time it was tough putting in left rudder when approaching the spin entry). Even my 1995 Typhoon needed this, although I did not do any incidence change at that time, I just did the idle to aileron mix. I think I remember doing a mix condition on my Dr. Jekyll so that with the gear up, and on high rate, the mix would go in (elevator). That way the elevator trim would not change on landing approach from what I was used to. I remember now that I also used to put in 1/8 inch left rudder trim activated with high rate switch for the spin entry. This would keep it from "breaking" to the right... but again, I digress...The issue with the idle-to-aileron mix- I found that the wings would (very slowly, like 5 degrees to the right) drift at/during the bottom of a pull out. Example would be at the bottom of a square loop, as the plane pulls out of a vertical down line to horizontal, (going fast) the plane would roll slightly right as its going fast...
So I discovered in 2003 the one application that I have effectively used negative wing incidence, but only on the left wing.
So the left wing neg incidence requires right aileron trim for straight and level cruise speed flight, and as the plane slows down that right aileron trim takes over, resulting in a nice straight, stable spin entry (either inverted or upright).
Here is a story. During the first couple of flights on my pro built FOCUS 1 1/2, I was ready to throw it in the trash because with the throttle to aileron mix it would be comical to watch. I'd be in stright flight at full throttle and then I'd quickly cut the throttle to idle. The plane would do a slow roll to about 45 degrees right. If I reduced the aileron mix so that down lines were fine, then it would not be enough throttle to aileron mix for a good spin entry. Needless to say I just started aggressively cranking in the adjusters on the left wing and after the left wing smashed into the top of the left landing gear strut (making a nice 1/16 inch indent in the bottom of the wing) the plane flew like magic. I screamed with joy. It flew to win the NATS.