The level of the boss relative to my characters and summons makes it easy to body block without too much worry. Keeping a shell of summons around Tan and not moving him too far from them at any point is important to make sure that he is able to get plenty of summon activations with conqueror mode even when the boss lays down fire everywhere and makes the map a pain to traverse. I may have been able to position Rho better for this fight because I was hedging my bets by making sure that he'd still be able to hit the boss regardless of whether it moved or not - didn't have time to predict whether it would. Rho's active is used in the third-to-last round as I am able to prevent enemy summons from spawning in the penultimate round, so I know my summons will be purely focused on attacking the boss, which means many procs of Rho's passive.