This score with Blitzcrank got me only A+? Is Riot screwing with me?

Just finished normal game as Blitz. It lasted 27 minutes. My score was 1/2/28 and I got only A+. Throughout the game I thought "This is S for sure, if not S+". My far worse scores than this got me better grades on other supports. So what kind of bulls**t is this? I assisted in first blood, put wards as often as I could, so WHAT EXACTLY were I supposed to do in order to secure that S?
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