SST,
Have you ever experimented with a tip plate that is a constant overhang all the way around, including the leading edge? I was,(am), going to try some tip plates on my two planes, an F90 and a Harrier 46 to see what effect they have on knife edge flight. I like your design. It looks good, and I guess the reason for not having them forward of the leading edge is to keep them from snagging in the grass should you drag one.