Dave, I hear ya about the coldwater applications with this fly. I've used it as a stonefly imitation/indicator while trailing a stonefly nymph underneath, and it's driven some rainbows crazy. I've also used the same fly in the pic with shorter legs as a hopper imitation.
I'll give your suggestion about the zonker-style tie down a try. I suppose that having the foam on top of the hook shank lets the fly sit lower in the surface film.