Rakan Support S Rank?

I'm having a LOT of trouble getting my final S token for Mastery 6 Rakan. I've had scores like 6/0/17 and got an A+? I'll go 2/3/19 and it will be a B+? I'm warding everything, I'm the initiate for every single team fight with my R and W, and I have NO CLUE what else I can do to break this glass ceiling. I read a few boards saying that if you want an S token to play the champ in a role they don't normally play, or to get the final hit on towers, drag (good luck last hitting that thing with a Trist and Kayn on team), or to get a lot of farm, make sure the match ends quickly... I just don't get it. I see ADCs go 6/3/9 and they get an S and I'm banging my head against the wall for my S. Anything else I can do or try? I got several S on Rakan before but it was before I hit my lvl 5 mastery, so they got "wasted" and now I'm having a hell of a time getting my final S. My duo que is a Mastery 7 Xayah and I'm sitting here with my dinky "mastery" 5 banner on Rakan.
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