I have noticed there is not mch difference if the enemies are behind you. They also tend to swarm in a circle around you, so its a little hard. As warrior, you will also have one of your most powerful emnity skills be an AOE cone, so you will want a lot of them to be in front of you though. The only positioning you really need to worry about is bosses. Most of them you will want to make sure they face you, but away from the rest of the party so AOEs don't hit them.