Thanks for the suggestion. I contacted VANS.
But I don't see much difference in my initial situation compared to the situation that various other builders had before they managed to get it correct. I think that there most be some kind of method or trick to it.
I also tried to clamp a large nail in the corner and tried to get the rib radius smaller so it better aligns the horn, but that is not really moving that much to correct it.
RV9 #92188 - Working on wings