I'm guessing it will have something do with:

--Some close call wins that weren't super impressive. problem is many other teams check that box too.
--Eye test. This one sucks because it's completely subjective and doesn't have to be justified. But it's the only thing I can see them resting on.
--Overall schedule/conference strength. problem here is Miami and Indiana and others have even bigger problems here than BYU.

At the end of the day it has to simply be the eye test. And nobody can ever dispute that because it's subjective. Lame.