I would imagine that in most years, if you finish in the Top 10 of the rankings you stand a good chance of getting an at-large bid, as I think it would be unlikely that more than 2 teams outside of the top 10 would get auto-bids.

On the flip side, I imagine that the Group of Five champion will generally always be outside of the top 10, and then if a contract bowl ends up teams outside of the top 10, that could eat up more spots as well.

For example, this last season if this next year's format was followed (and using the BCS rankings for reference), the Orange bowl would have ended up inviting #12 Clemson as it's ACC team since Florida St. would have been in the title game. Add that to UCF getting the Gang of 5 bid being ranked outside of the top 10, and add Baylor (Big 12 Champ) and Stanford (PAC-12 Champ) into 2 of the open at-large slots (since the Rose Bowl and Sugar Bowl are playoff games), and this leaves us with only 3 at large bids. Those bids would have gone to (taking the 3 highest ranked teams in the BCS rankings): #8 Missouri, #9 South Carolina, and #10 Oregon.

Assuming that this scenario is pretty typical from year to year, it looks like top 10 is really the goal in order to get into the top bowl games. If BYU were to finish 11-1 this next year, they would probalby finish in the Top 15, but I have to think they will be knocked for their SOS and probably won't be in the Top 10.