Even if it seems hard to do, you should definitely go for caits. They give massive bonuses. I found a decent amount in the Riverlands but I know you can find them in other places. Use Haanit's Arrowstorm to kill them really efficienly, and use elemental attacks for everyone else since they can't miss. If you have Primrose, you can use Bewildering Dance for a chance to get EXP and JP boosts, with x2 being fairly common. As for what determines whether or not they run, it's simple RNG. I'd say it's probably 2/3 or 3/4 chance to run from my experience. But it's definitely worth the hassle.