For one, if you are not supposed to fight them, it should be made less easy/convenient to just play with the LOS and shoot them down, as it is now. Totally immune to damage of most type? More HP? Whatever works, frankly.
Because right now exploiting LOS and taking few minutes to shoot them down is a perfectly viable (if inanely boring) solution and it that's by design... I'm not a fan.
Agreed. I would prefer them to be immune to all damage to make it real that they aren't meant for a fight.