The Mastery system for the rotating gamemode queue seems a little wacky.

So, I recently played a Legend of the Poro King game where I went 28/3 as Annie. This was very exciting for me, because not ONLY was this perhaps the best score I've ever managed in PvP, not ONLY did I get a Quadra, but FINALLY I was going to get a mastery token, something I've been after for over a week with no luck (and leaving behind a slew of A+'s)

But a 28/3 should definitely be an S+, right?

Wrong.

Got an A and 750-ish points.

Anybody else have a similar problem?