Ur doing it wrong then. You want to cast something like darkness, invisibillity, Blurr or Mirror Image on yourself before going into concentration. Once your Concentration Spell is up, your only job is basically to maintain it with this character.
In the beginning of the fight you can cast Darkness on your entire Group with another character. Then with your turn, you can move out of darkness, cast your concentration spell, and move back in. Also throwing a couple of summons into the enemies face can help. They usually stick to it, like a dog to bone, even on Tactician.
