Ah, I should have mentioned that I changed the angle of sloping of the wings, when I broadened them. The intention was to reduce the slope of the wings, because in my opinion it is way to steep.
Hopefully the image shows what I mean...
I think the overlap has something to do with the angle of sloping and that it could be solved by changing the angle of the frame just a little bit.
It seems to me, that the wings are not aligned exactly parallel and that is causing the problem.
Did you make similar observations?
I hope this is not to confusing...