problem is the more players you train the more spread out the training is, as you probably know.
If the players you are training are young and tall enough, sure some of them will experience pops but to be honest if you are training 5 positions, 10 players all at around 48 minutes, depending on sublevels i think you would be lucky to see 3 pops!
But remember that even if you dont get a pop the skill still improves. You know your team better than anyone else and so you can decide whats best for it.
gl man