@Riot: How does the grading work?

So I've been mastery level 6 on Udyr since the day it came out and I've been trying to get a second and third S or S+ ever since. However there's apparently something I'm not getting right. Take this game, for example:

https://i.gyazo.com/1f818888b307b2a2c7187e92b8fee839.jpg

That's an A?! Not even an A+? Is it my farm, because I was too busy farming champions to do wolves, and I've had plenty of games where I had a lot of farm, fewer kills, and low deaths and still didn't get my S. Most kills and gold in game, no deaths, second most assists, two drakes... I'm at a loss.

So what does the system look at for a jungler (or to make this thread more conducive for the entire community, what statistics does the system look at)? I know it compares specific champions in specific roles (the example given was mid Annie and support Annie are looked at differently). Do you take drag control into account? It's a stat I pride myself on, and it feels like it's not being taken into account. What about special cases? I absolutely love playing Udyr vs Kindred, because I just go where her marks show up and kill her, but it hurts my farm and map pressure.

Edit: Also, I never noticed the full AD Nasus with no deaths. But he didn't get an S either. He got that score despite being camped. He lived through a 4 man gank and got a kill out of it.