Using a level 4 trainer, trained half of the time 1 pos training, the other half 2 pos and team training (FT/Stamina), and one of my 20 year old P.All Star trainee got about 10 pops this season (excluding FT/Stamina pops). So I'm pretty sure if you go 1 pos training the whole season you can get a lot more pops than I did (way more if they're very young :P)
Doesn't matter how many players you train, it's the type of training that matters. 1 pos training lets you train max 3 (same speed if only 1 person gets training for example), 2 pos max 6 players.