I have a Roxanne which I love but still have not mastered it. I tend to flip my needles if I'm not careful where I place the needle... should be on the pad of my finger not under the lip edge (for me, don't know about others). I also have the deeply recessed thimble that Jean Brown uses and that is the one I generally go back to. I can't seem to use my thumb, although the Roxanne is supposed to be good for that, too. I alternate between using my middle finger or the first finger. First finger works good for going up a quilt and around curves.
But everyone is different.