Sigh, the default AI Key is different for each monster. If you leave the AI Key alone, and change the ATTACK RANGE (it's not actually called this in monster.csv), of the monsters, then the monsters will constantly swarm you, trying to attack you while it really can't because of soemthing you're supposed to change.
EDIT: Plus, stop asking questions and go try for yourself. If you do it right, you'll understand.