Is there a cap on Rating?
Ive noticed that after I obtained all four hextech chests for the month, my game ratings have been capped at A. Take as an example, I have obtained S- as Vladimir even though I lost the game and barely ended positive (7/5/1), but my recently game with Twitch only gave me a A rating even though I obtained a decent score of 13/0/6.
Is this a purposeful mechanism to prevent one from not being able to get a chest for said champion as they had already gotten S for him/her?