Please fix grading on supports

Hi I am a Bard OTP that just got in Plat. I have 75% winrate with Bard and would like the Mastery 7 so badly but I just cannot get an S or S+. During the previous game, I was so sure that I will get at least an S this time. 2/1/18 at 26 minutes! But yet again a S- ......... [slayer-jinx-unamused]

I think this has something to do with CS, because my friend was 2/7/8 with Ryze yesterday but still got S- because of his 300+ CS. I hope a Rioter will read this and think about fixing CS ranking with supports. Thanks.

[slayer-jinx-catface]