Champion mastery for adc's how much does cs affect it and does k/d/a matter?

I'm curious as to how csing affect's overall score for adc's. I just played an ashe game in 32 minutes I went 13/0/9 with 190 cs, figuring oh I so got at least and S, only to get an A+. and i was like what the 10/2 riven with 240 cs got an S I figured the fact of a perfect k/d/a and semi decent cs would enable an S rank. I asked a bit ago but cs score for mordekaiser but this time i'm curious about adc's. Any help is much appreciated.