SFF = Same Fanbase Factor
Normally if Link gets 53% on Cloud and then Cloud gets 53% on Snake, you can assume through linear transitivity that Link will get around 56% on Snake. This is the foundation that a lot of the xstats that we use are based on.
However, assume that Link gets 53% on Cloud and then Cloud gets 53% on Ganondorf. Well, you might believe that Link gets 56% on Ganondorf. However, as we've found, Link would overperform in this situation and score like 80% because Link and Ganondorf share a fanbase and people who play Zelda overwhelmingly prefer Link.
rSFF = Reverse Same Fanbase Factor
So if again say Link gets 53% on Cloud and then Cloud gets 53% on Ganondorf but then Link only gets 51% on Ganondorf instead of the 56% predicted, then we can that rSFF because Ganondorf overperformed.
congrats to BKSheikah the BYIG guru