There's nothing that says the top four have to be a P4. There's a chance the AAC and MWC could get two of the top five spots with both being ranked ahead of the Big 12 champ. Boise is already in front of every Big 12 team. So, that's not necessarily true but it would require Army beating Notre Dame, a top 25 Tulane, and Navy. Not a likely scenario but not impossible. That would probably be enough to jump the Big 12 champ. Especially if Ariz St were to beat both BYU and Colorado in the Big 12 championship game.