S with Annie (
So I started playing about 2 and a half weeks ago and am fairly decent. My problem is is my first main 
( i know i know ) I've done pretty decent with her but still am a nub. I need someone to explain to me how come i got an S- in one match and a A+ in another ( more kills, mobs ect. ) . I can see the match was almost doubled and my KD suffered a little but everything else i did should have balanced my overall score out. The only other real differences i can spot is my team, team gold average, and where my team was killed at. I just want my chest so i can possibly get 1 of the 2 skins i want so i can move onto my next hero ( 
). Does someone see something I'm missing , or keep doing what I'm doing and hope the match doesn't go too long.
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https://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2658082491/242505215?tab=overview ( A+ )
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https://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2656225447/242505215?tab=overview ( S- )
Decent games I get B+ - A+ it's starting to get frustrating
