Whew. Well, that was one problem, but there was another.
I had, intentionally, give the AI a neurosis about moving player allies out of the player's sight. But it was being a bit overapplied and actually stomping on some intended behaviors.
Joe, in the save you sent me now, in the newly "fixed" code, not only does Fotia properly advance, but the Nero actually perfectly positions itself to be able to keep a healing eye on everyone.
The only reason I say "fixed" instead of just fixed? Changes to pathing code of this sort can definitely have some interesting ripple effects. Only testing will reveal if there were any for this was. At least it's pretty localized: that neurosis only affects player AIs, and I only turned it off in a very limited number of circumstances. We shall see...