For me its totally different from one run to the next. Sometimes it's coated with monsters, sometimes its a ghost town. I've just learned to teleport in ways to move them about to be able to TK the chests (though Pit Lords' giant hit box is a pain in the ass). You can also hide behind the building structures on the edges of the peninsula.
My map very infrequently has boss packs on it though. Spawn density might have something to do with nearby features?
This. Changes drastically from run to run. Would be interesting to see if certain maps spawned them less though. I'd say ~75% of my runs have more than a couple monsters in there, with somewhere in the neighbourhood of 15-25% of those runs having at least one boss pack in the main area.
Just wanted to call attention to the bolded part. I use this almost every run when there are substantial amounts of monsters around, quite handy!