This doesn't really happen in my game. I do always use Mage Armor, and so Gale, Shadowheart, and my rogue all have roughly the same AC. But I have Lae'zel with 22 AC and even she gets attacked a fair bit of the time. Some of that might have to do with how I position my characters, though. Often I make it so the only character they can really get to or target is Lae'zel, by keeping the others high up, far away, or hidden.
