How do I get an S in the jungle?

I'm a {{champion:141}} main who's been grinding for that sweet mastery level. My most recent game I went 13/5/8 which equals to 60% KP, I had 82 cs at the end of the game which we ended in 22min. So when I got to the scoreboard I only got an A-. I kind of expected an S or S-, so what could I have done better that game to get that S? Is it purely CS you're looking for in the JG?
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