I'm willing to sabotage mine a bit in order to make an interesting story. 

Of course, something like that letter happens to be something that they would actually do. They think that they're untouchable, and some of them are proverbially still living in the past when Tin's cavalry hordes were unstoppable. Granted, their resources and sheer numbers make them a threat, but they're still more vulnerable than they think and far from invincible.