Can't help but feel like I got robbed on my champ score after having the game of my life.

Poro king, played morgana. Didn't die for 20+ minutes. Hard carried the entire game. Had over 6k gold 3 times before dying. 20ish kills / 5 deaths/ 40ish assists 2nd highest cs... Bought potions. What am I missing here? Easily S-S+ yet game gives me A+. I have gotten S+ on morgana numerous times in other formats for doing a quarter of what I just did. I wouldn't normally bitch about it in forums but having just completed probably the most dominate game i've ever had on a champ on one of my favorite champions, one where you turn to your buddy and break your hand giving him the highest of fives.... especially if you can get tier tokens in poro kings for S-S+ because that would have been my final one for 7 which would have been a hell of a way to complete morgana... I mean seriously something must be up. I have never been more sure that my performance in a game deserved an S than in that one (hell i'll even say that this was the only one that deserved an S). Guess all that will come out of it is the bitching will make me feel a little better.