Yesterday on Monza most I ever got was +4, either driving completely alone or having a tight battle in close proximity. There seems to be no further bonus for driving in a pack. It could help get back to the maximum after an SR down, I have also gotten +3 after getting punted to 13 in T1, receiving a 5 sec yellow flag penalty and climbing back up from 13 to 2.
Most I've gotten on a clean daily C race was +13. Daily C is the place to be to get SR up.
Least I've gotten on Monza yesterday, -24, after repeated punts into cars in front of me resulting in getting a time penalty. Hitting a car in a way that you receive a time penalty seems to be punished hardest, the game doesn't care if you get hit from behind into another car. Another race I was first punted into a shortcut at T1 yet saw now penalty for that (the game does sometimes recognize when a short cut is not your fault), and a 2nd incident where I hit a lagging 1st place that suddenly starting braking way early for no reason and got a 10 sec penalty while he survived it fine. Result -14 for those 2 incidents.
Most of the time though just getting hit in T1 negated any possible gains and a neutral rating was all I got. I never got any time penalties from short cuts, always stayed on the road. However when the hit at T1 was hard enough I didn't get penalized for it and could still end with a +4.