I have never seen anything published about incidence of tip floats, but one of my buddies made some floats once and accidentally put negative incidence in the afterhull. Once they touched the water, they stuck and there was nothing he could do to get it unstuck. Customarily they seem to have just a bit more "nose-up" than the main float. I tried hydrofoils once, and they worked fine once I was moving along but since they had essentially no floatation, the plane did not taxi well.