I just wanted to comment regarding the rule you mentioned and wanted to say that I was always told that, unofficially, you can always move up but only a tier at a time and you don’t want to move down if you can avoid it because then you likely have to move back up. The calculus does get harder though the longer you’re in the game — you might elect to move down because you’re significant other gets a promotion or you don’t want to uproot your family, etc.
For sure, they aren't hard rules. There is also the aspect that locations matter to some people. It's worth noting though that universities have a unique negotiating token, in that you can also negotiate for a job for your partner as well. I think universities are often forced into this because of the natural location constraints.
