I don't know if anyone has ever told me to avoid touching the palm. When I toss, the ball might be touching the upper part.At clinic yesterday, one of the coaches was trying to help me with my dismal toss. He suggested the ball should rest on your fingers and not be touching the palm at all. Suddenly my tosses were a lot less wild - not perfect, but at least reasonably in range. Seems like such a simple tip that I can't believe nobody has told me before. Or maybe they have and I've either forgotten or wasn't really listening.
The more important concept for me is one of the platform: you want to "raise" the ball up to the right position rather than throw it, sort of like if you're lifting something to put on a high shelf. I think a lot of variability enters when using more fingers and wrist as opposed to the arm [relatively straight but not locked].