Personally I feel they should go by rankings, regardless of what conference the team is in. For example, a team ranked #8 should never go to a worse bowl than a team ranked #15. Otherwise, whats the point of rankings ? Might as well just throw the rankings out and just have rankings for the top 4 teams.
That hasn’t happened since the old days prior to the BCS. The BCS and Power 5 created alignments for bowls with conferences. Used to be that the best matchup to draw fans was used such as the January 1992 Peach Bowl with ECU/NCSU.
The BCS relied on a combination of polls and computer selection methods to determine relative team rankings, and to narrow the field to two teams to play in the BCS National Championship Game held after the other college bowl games (the game rotated among four existing bowl games from the 1998 to 2005 season, and was a separate game from the 2006 to 2013 seasons). The American Football Coaches Association (AFCA) was contractually bound to vote the winner of this game as the BCS National Champion and the contract signed by each conference required them to recognize the winner of the BCS National Championship game as the official and only champion. The BCS was created to end split championships (such as 1990 with Ga Tech and Colorado, 2003 Southern Cal and LSU, 1997 Michigan and Nebraska) and for the champion to win the title on the field between the two teams selected by the BCS.
The BCS system also selected match-ups for other BCS bowl games (New Years 6): the Rose Bowl, Fiesta Bowl, Peach Bowl, Cotton Bowl, Sugar Bowl and Orange Bowl. The ten teams selected included the conference champion from each of the six Automatic Qualifying conferences plus four others (two others prior to the 2006 season). The BCS was created by formal agreement by those six conferences (the Atlantic Coast Conference (ACC), Big East [now the American Athletic Conference (AAC)], Big Ten Conference (Big Ten), Big 12 Conference (Big 12), Pac-10 [now the Pac-12 Conference (Pac-12)], and Southeastern Conference (SEC) conferences) and the three FBS independent schools, and evolved to allow other conferences to participate to a lesser degree. For the 1998 through 2005 seasons eight teams competed in four BCS bowls.
It had been in place since the 1998 season. The BCS replaced the Bowl Alliance, in place from 1995 to 1997, which had followed the Bowl Coalition, in place from 1992 to 1994. Prior to the Bowl Coalition's creation in 1992, the AP Poll's number one and two teams had met in a bowl game only 8 times in 56 seasons. The AP's top two teams met 13 out of the 16 seasons when the BCS was in place.