any base on the ground can be targeted. Water is not 100% safe anymore, it will increase the dificult a bit but they still can do. High rocks, is more safe, but after meteor shower it can be targeted too. All it could be solved not letting purge damage pieces that is not owned by who triggered it. The same for zaths orb exploit the spider should not aggro on your own ilusion, and thralls should not aggro to ilusion on pve.