For me, they've made this too complicated. It's not complicated at all.
If the ref thinks a player has intentionally placed his hand in the way of a moving ball, and the ball strikes anywhere from the bicep down to the fingers, it's a foul.
The ref has one chance to see it, at pace. He has help from the assistant, but he makes a decision based on that.
Why they feel the need to expand the rule or make changes is beyond me.
One thing the FA should clamp down on is player power. They brought the rule in about players who wave an imaginary yellow card will themselves get a yellow card. That worked and very rarely happens now. They should stop players from raising their arms to influence offsides, and there should be zero tolerance of players arguing with officials. Arguing has nothing to do with the "passion of the game". Look at rugby. Players are pumped up, but how often do they argue with a ref over a decision? Almost never. Football is prima Donna sportsmen who think their opinions matter.