Attacking someone from the rear is already in the rules. If you attack someone who cants see you; you get advantage. Its not taken from Divinity at all.
Height giving advantage I could have sworn was in the book somewhere but cant for the life of me find it. Height also imposing disadvantage on you if you attack the one higher up though is sheer overkill. It makes the game lean so heavily on having higher ground if you want to succeed that it becomes silly.
