Sometimes it is even worse. The ogres don't go back to their spots. They just stand still with their backs to the group. And somtimes they immediately go into the other direction, if I do so (Not, if the fog of war touches them, like other creatures do). So the group has enough time to finish their turns and shoot again. I don't want to exploit their behaviour. I just want to run away to keep some distance to them (If I have no tank in my group, they would be too strong to directly attack them). I think my strategy is fair, because in real life, if I had to kill a slow and strong creature, I would do the same thing. But they should have a real chance to catch me or do something against my strategy. If they behave that stupid, they could as well stand still and wait for me to kill them. Somehow they have to react in an intelligent way. The Ogre Druids try to catch me with Tanglefoot or something. But mostly they get stuck themselves. Maybe they could do a little sprint and try to engage one of my group members. But if they do so, they are a little bit exhausted. Something like that would be pretty cool. Different monster could have different behaviours for that situation.
PS: I think being able to split groups is a good thing. But it is too easy because of their stupid behaviour.