Pls share your expected results? What do you want to achieve finally?
The dashboard I am creating will eventually be accessible on a tableau server to all the employees in my company. The value, represented in my example as the sum of the customers, is actually an important company metric. The values I want to display need to be filtered as I specified above in order to be correct. I cannot share the actual data and the actual metrics are quite complicated to calculate. I was able to figure out how to calculate them save for this filtering issue, but I simplified the example to only provide relevant information.
Edit: as I stated in the question: "When the dashboard is showing both A & B, I would like to filter R and C such that R can be anything but C is only including blanks. When the dashboard is showing either A or B only, I would like to filter R and C such that C an be anything but R is only including blanks."