From what I can tell it is a dynamic system, which considers the longevity of the poster, the number of quality posts that aren’t ever mobbed, how long it’s been since they have received mob votes, and probably a few other things. The higher those rates the higher the threshold is for them to get the mob ban. I’ve seen posters done in just 60 votes, and I’ve seen guys withstand over 130.
Its a neat system. The board has a good reputation for self policing itself.