With the help of Dan, who I fly with, I think I have got power launch working well now. I have settled on about half power. On one launch I had too much power and my thumb was pushed through the A triangle link and got stuck!
I've found the best way for me is to be set up with A's just held taught, Then lean forward enough so that the prop blast does not hit the wing. Put throttle to half power. Then start to run and straighten up at the same time so the prop blast now launches the wing. Video below yesterday.