OK, have just been adjusting as per the video, but I think the issue lies with the extension. The guy in the video has an S bend extension that keeps the stick not far from the centre. My Z extension displaces it 150mm to the rear. So there is no setting that works to keep it in place, once you go past centre point against the displaced weight. I can get it roughly to stay but there are certain parts of teh range of movement where no amount of slider setting will offset the weight of the displaced grip.