How does the end of game scoring work (D/S+) (1/1/39 A+ VS 1/1/24 S)

I made a post about this a few days back when I got an A+ on a 1/1/39 game as Yuumi confused as to why I didn't at least get an S-. Just finished another ranked game and went 1/1/24 and got an S?? I now have NO IDEA how the scoring system works. Looking for Riot Admins/Mods to hopefully explain why such different KDA got such different scores. I know its just a score that they give you at the end of the game and it doesn't mean anything but like, c'mon...
Report as:
Offensive Spam Harassment Incorrect Board