my opinion is that if lets say, we train a player in 1 position and he get 48 minutes (48+) that is a 100%, but if youre training the same player in 2 positions, he gets still about ~60% , so we double the trainees and in total get more up's. I think the only time that getting only 2-3 players to train on 1 position is when you're training them for the national team and u21, thats my opinion :)