Only got an A+ from going 26/3/9, having taken 4 drakes, stole baron, got FB, quadra kill, and 12 KS

Here is the details for the match: http://matchhistory.las.leagueoflegends.com/es/#match-details/LA2/413304240/422240?tab=overview I was the Nocturne. CAN I **PLEASEEE ** GET a **RIOTER ** to explain how this isnt a S+ performance? I gotten higher gradings with only a quarter of the kills and objectives i got. highlights i did this game:

1. First blood at lv 3 in toplane
2. Controlled all the drakes (4), including having stolen one with my ult
3. Killed Baron
4. Helped kill almost every tower, including the first one
5. Maximum of 12 kill streak
6. Got a quadra kill near the end of the game
7. Finished 26/3/9 (2 deaths where sacrifices to steal objectives... with success)
8. 83% kill participation

But apparently, this only neted me a A+ in the performance ranking. Click to see image I feel seriously cheated and de-motivated. Ive been trying to get two more S on to get the Mastery 7, but every time i get a good game im given this BS rating of A or A+ even in games where im nearly flawless. Can a rioter PLEASE explain to me why all the things i did this game didnt qualify for a S? Its seriously frustrating as hell.