If your gain is defined as T = To+Tm where To is the original and Tm the marginal and the loss is defined as L = Lo + Lm when LO is the original loss and Lm the marginal, then T/L = (To+Tm)/(Lo+Lm) ~ Avg win/avg loss from (To+Tm)/(Lo+Lm) you can solve for Tm/Lm provided you know the value of the ratio. One equation, three unknowns here, Tm, Lm and T/L