Spawn pattern's resulting in Rare Boss's

[vg_geek86]

Tried doing a search but kept getting an error =(.
When doing the relics quest on Parum some1 brought it to my attention that when certain enemies spawn at certain blocks, they're will be a rare boss at the end. I know it works because the guy knew when certain enemies would spawn including rappies b4 we even got there. Ne1 know the pattern, or could point me in the right direction?

[Dj_SkyEpic]

http://psupedia.info/index.php?title=Rare_Monsters

[vg_geek86]

My thnx =)