How to get more alien immigrants?

[AcetheSuperVillain]

I have a bunch of mods that introduce alien races.  Faction bases are overwhelmingly alien, but slaves and immigrants (wanderers, rescue requests, etc) are overwhelmingly human.  Some aliens never seem to show up at all, Zoltans and Engi (from Lighter than Fast) show up as factions but never as aliens or slaves as far as I can tell, and Ferians and Daleks don't seem to show up at all, unless they are selected as initial colonists.  Xen's animaloid races, Xenn, Logann, Racc and Ferex work satisfactorily. 

Is there a mod out there that reduces human immigrants, or is there a variable somewhere I could tweak to make the humans less common?