How many times do bosses usually spawn in a Simulacrum run?

I got Kosis on round 18, 19, 20 today. No big deal as I take him down in 20 secs.

But would of drove me insane earlier in league.

It definitely varies. I've had runs where I'm surprised to barely see them and other runs where they show up sooner than expected (and more often).

Typically all my runs have at least one of each, sometimes I get two fatties. Kosis definitely seems to spawn in the 15+ waves, don't think I've seen him in any earlier waves myself. Also, in my experience I've always gotten just 1 delirium uniques per simulacrium regardless of how many boss spawns I get.