There is a reduction. It can be a bit confusing at first, but remember that a skill that trains 1 position (Passing for PG, Inside Defense for C, etc.) is 100% training.
Anything that trains 2 positions (Jump Shot for PG/SG, Rebounding for PF/C, etc.) is ~70% training in comparison to training a skill that only needs 1 position.
Side note: these percentages are assuming that the player being trained play at least 48 minutes that week in that position.