Where I live, if a bus gets late enough (or too full) and the driver knows there's another bus right behind, they'll start skipping stops. I don't think that would help in this simulation because people getting on seem to be equally likely to want to get off on each stop, but IME that's not really accurate for most bus routes. People want to get on the bus at all sorts of random places, but 90% of people are getting off at the same two or three stops (transfer point, city center, etc). It would be interesting to see these things would affect the bunching, I think.