Hang on to your hats: It's going to get confusing.
For the first two games, Tindall (a QB) was my RB1.
For the first game, I had a universal fatigue setting of 30.
For the second game, I had a universal fatigue setting of 50.
Tindall had every offensive snap at RB the first two games. Nobody else got on the field.
For week three, Slater was my RB1 and Tindall my RB2. I also changed the fatigue settings to position-by-position. Slater had 12 carries, and Tindall had 8.
For game four, I've moved Tindall back to RB1 and Slater at RB2. I'm leaving the fatigue set to position-by-position.
Hilariously, I won the first two games and got blown out in week 3. I forgot to blow on the dice.