Regarding the question about keeping the diver's head back -- one of the things you do during an unconscious diver recovery is try to keep the reg in the victim's mouth. I can guarantee you that, if you are above them and managing their buoyancy and yours with their inflator with one hand, and trying to push the reg into their mouth with the other, you WILL push their head back.
On our OW rescues in various classes and scenarios, you almost always end up much closer to vertical than to horizontal. In cave, it's different, because you aren't ascending, per se, but rather swimming forward and somewhat up.