Can anyone think of a reason why the attackers would go past the defenders before attacking them?
The fox generally goes just past a defender and the lizard will go about two squares beyond before stopping, going into attack mode and then the defender will eventually disappear.
The box colliders are packed tight around the attackers and are the size of a world unit square on the defenders.
When the lizard eventually stops the two box colliders (of attacker and defender) are no longer in contact.