The training club has just arrived and the feeling I get from it is a slightly shorter left thumb than I've been using. It's arrival here in wet Wales has coincided with a monsoon so I haven't ventured out to hit any balls yet. I think the left thumb position is quite important because it affects the amount of hinge you get. I've used a long left thumb as a band aid to prevent a bad case of the hooks on the course in the past - before discovering this method of course! I'd be interested to hear other views on this.