Mob density definitely has an influence. As I understand it, there’s a minimum treshold, and monsters that grant more XP/Infamy give more progress towards the treshold. So it’ll take longer if you only kill trash mobs instead of heroes and bosses.
I don’t know if Nems spawn immediately once the treshold is met, or if there’s a random chance on each additional kill. Or maybe the minimum treshold is randomized each session.
As far as I know the requirement to spawn is variable with each game session (sometimes more, sometimes less). They spawn much faster in Challenge areas so be sure to kill enemies in those to get them to spawn quickly.
Kaisan spawns usually before the key door for me going for Morgoneth. Rarely does he not spawn before the door.
Same goes for Benn and Grava when going in the Bastion of Chaos. Usually at least one before the key door and sometimes both!
For Kaisan, the spawning kill require is 280-855 on Normal, 240-735 on Elite and 160-490 on Ultimate.
Before v1.2.1.5, this require is 160-490 on all difficulty.
There has been no change in the data on Ultimate.
But I heard from others that it is more difficult to spawn Nemesis than before. I’m not sure if there are any hidden changes that I didn’t notice.
So the XP granted for killing a monster has nothing to do with it, only the kill itself? Say for example if I want to spawn Chthonian Nemeses, killing 160 Chthonian Hungerers gives the same progress as killing 160 Obsidian Ravagers?