Any team that plays anything like a credible schedule and goes undefeated will be top 6. That seems to be the glass ceiling for good non-P5 teams.
Since 1980, BYU has had only two one-loss seasons. They finished both in the top 10 both times and didn't start the season ranked either time.
The seasons prior to both these Top 10 finishes BYU was 8-4 and 7-4.