the eles always spawn to the front left and right of Cho. you can force the eles closer to the boss by facing him against the wall, but this introduces other issues. imo if melee uptime is a concern your best bet is to have the tank run the boss back and forth between eles for cleave
I don't think intentionally gaining corruption is the move for progression. But if it's what gets asked of you, in phase 1, standing in the pools placed by the corrupting adherrents is probably the best way to do so (then just before you reach 100 corruption, duck out of the pool to get healed to full before running back in) - just be mindful NOT to do it when either oozes are spawning or the boss gains empowered shadows.
Adding another comment because I think I've changed my opinion on this. If done well mages do A LOT of dam. Also I was wrong about the best way to gain stacks. Try to get to 25 corruption by standing in corrupting crash, or if necessary you can stand in the pools. Then, once you get the accelerated corruption debuff, be sure nobody dispels it. The debuff should bring you to 100 corruption in just under 40 seconds without doing damage to you. As far as I'm aware, this is the only way to become fully corrupted with full health.
