Grade system

Hi there. Since the introduction of the grade system, which indicates how "good" a player fulfilled his role (that's how I understand it), I'm generally confused. But know I experienced a particular odd result and I really am in dire need for someone to explain me how this all works. I played a round of ARAM and after the match I compared the grades of another player (of my team) with mine. Here are the (most relevant?) stats: **Me (Veigar):** Level: 12 KDA: 8/1/16 Gold: 7,657 CS: 31 Total damage to champions: 8,928 Grade: A **Player (LeBlanc):** Level: 11 KDA: 7/3/13 Gold: 7,387 CS: 26 Total damage to champions: 7,000 Grade: S- In summary I was better in every statistic. The only thing which sounds plausible to me as an explanation would be that the "difficulty" of a champ is an important factor in the calculations. Can anybody confirm this? PS: I didn't even try to use the board search because I don't have the nerves for such a mess.
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