Calculations as shown in such articles miss one point. They use simple arithmetic to calculate residuals, but in actuality the process of washing is dynamic and requires calculus. I have posted Mason's equation at least two if not 3 times here before that shows the actual relationships obtaining in washing. The final result is a function of dC/dT or the change in concentration vs time. This is what confuses the issue. Particularly since there are influences on this by the amount of residuals leaving the film and the amount of residuals trying to re-enter the film (or paper as the case may be).
This is why a practical result is always so much better than the math model.