OK, I've looked at this again, and I think Nanda has a point.
One simple example. In my last game, against Jorvik Celtics...
(2417757)The team matchup rating says that my team from the SG position scored at a rate of 82.9 points per 100 shots.
My two SG players were Eric Dickinson (who scored 16 pts from 18 shots) and Rudolph Al-Shurman (who scored 13 pts from 12 shots). Individually, they would have a scoring ratio of 89 pts per 100 shots and 108 pts per 100 shots respectively. Bearing in mind that Eric took more shots than Rudolph, the team's overall scoring rate in the game, from the SG position was 96.9 points per 100 shots (29 points scored from 30 shots).
The team matchup rating figure for shooting from the SG position is lower than either of my players actually acheived. So something must be reducing the team matchup rating.
Even allowing for Free Throws I cannot find anything to explain why the matchup rating is so much lower.
Note that this is not about tactics or anything, it's just a maths question. How can the SG matchup rating give a points per 100 shots of 82.9 when my actual SGs were both shooting a better rate than that?
In other words, what other variables go into calculating that 'points per 100 shots' rating? It clearly isn't just a reflection of the SG's scoring rate in the game...