I've always had a hard time with this technique. My back is not particularly flexible and I am large. When I wedge myself under for this technique I find that I threaten the straight arm lock to the point that I don't feel safe. It would be better if I could fold under the person more, but because I can't I tend to force them up off me a little. Even from there, I'm threatening the straight arm just by reaching under their leg. Anyone have any advice?