Champion Mastery is biased against tank junglers

I just played a game as in jungle and went 7/6/30 but got a B+. One of my friends went 6/1/10 on in jungle and got a B+ as well. We did well in our games. We engaged, we peeled, we did our jobs well but got mere B+'s. I don't know what the criteria for doing well in those roles is, but there should definitely be some changes.