Tuesday's Cincinnati round of 32 pits Marta Kostyuk against Sloane Stephens on hard. Marta Kostyuk comes in at 8 wins from the last ten. Sloane Stephens comes in at 4 wins from the last ten.
Marta Kostyuk simply rates much higher on hard, and our number follows from it. Stephens needs several things to break right at once; the percentages say they usually don't.