That's all? I thought it was a bit more than that.
I do not know 100% for sure. But after having a level 6 trainer for a long time (with one position training, even), my suspicion is it not make the difference that people think it does. Of course, too much depends on what you are training, how many positions, how tall, etc. to really know anything for sure.
In any case, 4 pops per player is still an extra pop per season. That can make quite a difference on a U21 player (think of the difference between 9 and 13 outside d).
Run of the Mill Canadian Manager