between the helmet & shoulder pad — & that the players are more or less stationary.
It's a really, really stupid rule imo. As long as the guy's arms are extended & he's not hitting high, how his helmet makes contact in the tackle should matter zero, imo. Dudes should have a right to endanger their own well-being in a game as naturally violent as FB. What SHOULD be done to control that is simply the correct coaching of safety in tackling & blocking technique. That was something more or less lacking in the formal coaching of FB before the last decade.
In regards to personal safety, change the coaching, not the rule book.