Where can I find a clear description of the points system?

Sometimes when I win a game I get 10 season reward points. Sometimes I get more. Sometimes when I lose a game I lose 10 season reward points. Sometimes more. I can’t figure out the rhyme or reason to it and I don’t see a description of how the points work. We’ve got 8 days left to the season and I’ve got 3218 points. I decided to start another async game and got paired with someone with phobies way beyond my level. So clearly I’m going to lose this game. Yet will I lose 10 points and still be in tier II for Sum of all Fears? Or will I lose 18 or more points and drop down to tier I, ruining my whole month’s worth of effort?