This is how I understand that it works now:
Let's say that you are training something like Outside Shooting.
You can train SG; PG/SG; SG/SF; or Team.
So if you train SG, players at SG get 100% of the training.
If you train PG/SG, players at PG get 50% of the training, and at SG 50% of the training. This is my guess, anyhow. Since you are training more players, each gets less benefit.
It might be that if you train 2 positions it is a little more efficient, and players get 60% of the training they would get if you trained SG. Or conceivably it could be 65% for SG and 55% for PG, since it would reasonable for OS to benefit SG a bit more than PG.
There would probably be a similar distribution for SG/SF.
For Team, it could be that each position gets 20% of the training that they would get for SG alone, since you can train 5 times as many players. Or it might be that there is a little bonus, since it may be more efficient to have everyone practicing their shooting, rather than two or 3 SG, with the other players simply shagging rebounds.
Here is what I am proposing:
For any training skill you can specify any of the following position focuses:
PG
PG/SG
SG
SG/SF
SF
SF/PF
PF
PF/C
C
But if you train a single position, all positions get some benefit. Currently, if you train SF, the SF gets 100% of the training. But I'm saying instead that if you trained SF, that the training would be distributed among all 5 positions, perhaps like:
PG 5%, SG 15%, SF 60%, PF 15%, C 5%
That is "SF" wouldn't mean train only "SF" and ignore totally the improvement of all players on the team, but rather it would be focused on SF with some benefit to the positions, especially to the positions that are most similar.
If you trained something like SG/SF then those positions would share the focus, but the other positions would still get some training.