I think you get it but didn't really go far enough in the description to define how definitive that contract is.

When the Rose/Sugar are not the semi-finals they absolutely are tied to a conference.

Rose = B1G/PAC
Sugar = B12/SEC

And that tie is not just to the conference champion. If the conference champ of those conferences are selected for that years semi-final games then the next highest ranked team in those conferences (2nd place) will go to those bowl games. They DO NOT become at large spots to other participants if the conference champ is in the play offs.

In fact if there are 2 teams from a conference picked for the playoff semi-final games then the #3 team from that conference will fulfill that conferences contract with the given bowl game.