Yeah I've sussed the moving of the Anchor point for snapping, but having two, one to lock an anchor point and one to stretch / shrink a scene would be really handy.
I think I've sorted it now. I think my problem had more to do with me not understanding how SU & LO interact with each other.
Making the changes to the shadows in SU then updating the scene via the Scene dialogue and then saving the model in SU seems to update the view/scene in LO.