Does Mastery ratings change for position?

I main Trundle in the Jungle and can do very well as in KDA wise. I also help the team out a lot with ganks and trying to get Drag etc.... But I still can't get higher then a S- when i don't even die. As a Jungler you aren't going to get a high cs count unless that's all you focus on. Does the mastery system just base off of the champ all together because that's stupid. It should be by position.