Well, it could be something to do with the fact Aerie has the second lowest Constitution in the game, 9 (narrowly losing to Viconia, with a measly 8!). By comparison, I always find Imoen gets carved in any close quarter fight situation, and she's Con 16 and Dex 18 (as opposed to Aerie's 17) AND Imoen wears Elven chainmail. Go figure... Plus, of course, as a Cleric/Mage, she gets a piffling amount of hit points whenever she levels up.
Life's just not fair...
Let me get this straight. The journeying outcast Drow-of-the-road Viconia has a Con 8, but rich-kid, naive-view-of-the-world Nalia and backstabs-spells-and-archery-are-my-specialities Imoen have Con *16*? They're as tough as Minsc! Come to think of it, a lot of these stats don't seem to make much sense...
Tancred
"I don't kill people because I want to, Brother. It's a holy duty."
- Sarevok