actually, "evasive" sounds more like a tag that can be added, not a full on AI.
if added to the other AI's, you'd get these results:
passive - when you attack it, it runs off
passive-aggressive - if you attack it, it will attack back for a short time, then run off.
aggressive - it actively pursues you, attacks for a small bit, then runs off (but will then make guerrilla attacks on your troops in the area, attacking and running off)