I didn't think their was a height calculation in the game? Has that changed?
Something to keep in mind: as in the real world, younger players will improve more quickly than older ones, and taller players will train faster in some areas while shorter players improve faster in others. You'll have to take advantage of this information to optimize your training routine.
That really seems like a wash, your later training in whatever is slowed down by just as much, plus you get your skills out of whack, which gives you a penalty to training. Basically, there are two paths, going with balanced training (my strategy) will result in a slightly better player, but will waste some resources getting there. Doing all of the single position training first will allow you to focus resources more effectively, with a loss of a little bit of training efficiency, due to out of balance skills. There is of course also a compromise position, where you do mostly one position, but during the allstar week and other weeks with only two games (offseason) you do two position training.