Infested Valley boss not spawning ritual circle

Trying to bottle this boss for Ritual Encounters V. I ripped through dozens of maps without seeing the boss room have a ritual circle once. Is the spawn rate on this messed up?

On a side note, why is it that when you do get a ritual circle in a boss area there is still no guarantee that the boss will actual come out? It's a bit annoying having to watch who actually spawns when I'm fighting the ritual. Can we either have the boss always come out when the ritual circle is there or at least make it so when you hover over the ritual station at the end of the fight it tells you whether the boss is there or not?