Players are players, and not part of the field of play. They are either in the field of play, or outside the field of play (foul territory).
player position doesn't matter. Where the ball is matters. Especially when it comes in contact with a player or other object. If top of fence is a homerun, it needs to be indicated in some manner. Even putting the yellow paint on the top of the fence is crazy. It's a simple rule. If it goes OVER the fence it is a homerun.