Get a couple of LP back for getting an S or S+ rank?
I think if you lose a game but got an S or an S+ that maybe it would be cool to get a couple of LP back for your loss for doing good stuff all game. I know it's sort of hard to judge what you were doing with how the system works, but I think it would give players an incentive to not drop everything and give up when they're behind as well. As well as giving the grading system a little more impactful meaning.
Just a thought I guess.