To do this properly you need to make sure you don't have any extra players sitting on the bench. If someone isn't listed in the lineup at starter/reserve/backup but is still active on the bench in the game, they'll come in during the 4th quarter in blowout situations. I generally use 2 players at a position, 1 as starter, 1 as reserve and backup. For positions I want 48 minutes for one player I list them as you did, starter/reserve/backup all three. Then make sure anyone not listed is moved to the inactive (right) side at the top of your set lineups page, and you should be in good shape assuming no foul trouble or injuries.