another thing I noticed is no matter how many waves the "Troublesome Customers" advertise they have it's only 2 waves. I don't use my mercenaries at all really because I always end up only fighting two waves.
edit: I got rid of all my mercenaries since I end up fighting the waves manually every time anyway. It's irking that the mechanic doesn't work as it would appear. So far as I can tell, having no mercenaries vs having some doesn't augment how often you get invaded. They are really only there to maybe get rid of a couple waves but since the waves seem to be locked at 2 for me they are useless.