There are going to be not 1, not 2, not 3, but 6 (yes SIX) at-large spots in the NY6 bowls this year. One will go to a G-5 team so really there are 5. There is no way a 12-0 BYU team gets passed over for 5 other P-5 non-champions. These teams will most likely have multiple losses. I don't see a scenario where BYU goes undefeated and is not top 10 and does not go to a NY6 bowl.
Maybe you are confusing NY6 with the playoff. I would also say that BYU will not be in the playoff this year unless all mayhem breaks loose in college football.