[thejeff]

Shift-I gets you the monster id, not the unit Id. As far as I know there's no way to actually see the unit ids. Anywhere.
You can figure out relative order, but not the actual numbers. I'm sure there's a connection between unit id and how the troops are initially positioned in formation, but I've never bothered to look into it.

You can't give troops stay behind troops orders.

I have not had the problem with flying archers. I've even been playing around with Caelum recently, though EA and thus mage rather than archer focused. But they've never done the suicidal charge.
In fact I've never seen flying archers fly to get closer. If they're out of range they walk forward.

Jorus, is this a MP game? Can you post the turn? Maybe someone can see how to make sense of it if they can actually see the fight.