Is it not possible to get an S in every game?
It seems that sometimes certain players will have perfect KDAs, win, and be unable to do any more than they did - but still will not get an S. I conjecture this is due to the champion mastery deciding on scores based on how people do with the champion in other games of similar length, which makes it impossible to get an S in low scoring games while still playing perfectly.
The game that inspired me to make this post is attached.
Jarvan IV and myself on Taric both had 70% kill participation and zero or one deaths, yet we were both given an A+. Ashe, however, received an S-, while only being involved in a single additional kill while having an additional death. What more does Riot expect out of players to get an S?
i've played whether or not my team won.