Are you describing a situation where you only have 9 players dressed for the game? In this case, there are often many things you could do with your lineup that would result in a player staying in for all 48 minutes fairly consistently.
However, the main point I was making is that if you dress 10 or more players, and are winning by more than 20 points in the 4th quarter, all 5 starters will come out of the game. It doesn't seem to matter what you do in terms of depth chart instructions, or where you place backups and reserves on the lineup card. This is why if you think you may win in a blowout, dressing only 9 players helps ensure that one trainee will stay in for a full 48 minutes. If you want to force 48 minutes at 2 positions, you would want 8 players, at 3 ppsitions, you would want 7 players, and so on.