I understand your question, but that's just not how it works, you can tell from experience.
SF S. Horák 10 - 21 0 - 1 1 - 2 +24 2 9 6 2 1 0 4 21
PF M. Tadic 6 - 11 0 - 0 0 - 0 +20 3 15 6 1 0 1 0 12
Pretty similar performance, except for the higher rebounds for the PF and the higher scoring for the SF. Only the 4 fouls are blemish, but they don't have too much of an impact on ratings. You'd think they'd have about equal rating, since they performed about equal. The SF got a 9.5 and the PF 13.0. That's because the SF played more minutes and has lower skills.
SG J. Dézsy 39 10 - 21 1 - 4 3 - 4 +17 0 1 4 2 2 0 1 24
SF S. Horák 42 8 - 16 0 - 0 7 - 8 +13 3 9 3 1 2 0 6 23
Same thing, now with equal minutes. Only the fouls again, but offset by more free throws and rebounds. SF 9.0, SG 13.0.
Other times you see guards with very bad stats in 30+ minutes, but still with high rating. That's usually caused by the fact that they don't have any good inside shot but the team is running Look inside. If that guard gets the same stat but in an outside offense, he'd get 1 or 2 points higher rating. Not because of the better stats, but because his skills are better in an outside offense.
A game of a friend of mine:
SG A. Voorhoeve 48 13 - 22 2 - 3 5 - 7 +50 3 7 9 1 0 0 0 33 8.0
PG A. Sela 21 3 - 8 2 - 5 1 - 2 +24 2 3 3 1 0 2 1 9 10.0
33-9-7 with just 1 TO in 48 minutes, 59% FG% and 2-3 threes and no fouls? How does this guy get just 8.0 and the PG a 10? Minutes played, skills (9k vs 30k salary), and the PG is actually an SG so he would have gotten a higher rating if he played his natural position. Performance doesn't influence rating.