What you might want to try is a 2 part AI.
The first is the standard stuff for one entity.
*move toward target
*move away from target
*shoot at traget

The second is a group AI. It can effect the or override the result of the
first AI. You attach entity to this groupe and thy strat reacting differently.

This type of thing was being fooled around with by the guy who did the AI
for Black and White. {think I saw a link off slashdot}

Does this help or just complicate things for you?

Armand