You can only get so much offset, regardless of clamp used. Perhaps you are trying to offset too much? If the bow and the arrows are tuned well then you really don't need maximum offset with maximum helical as some would have you believe. Get enough offset so that your vanes stay on and call it good .

If you are using a dropaway rest then I would suggest using a right helical if you are going to go that route. That way the arrow spins in a fashion that will cause the points to tighten as opposed to loosen. If you are a lefty shooting off the shelf then you will probably have to go left helical.