I'm not sure if I quite got there, and I'm not sure if my mock set-up
matches your quintiles, but maybe the general concepts could be useful for you.
Once you have your Quintile5 flag, I think you'll need use a table calculation
to get it to hold for that person during the filtering process. I used:
The attached graphic shows the Addressing and Partitioning that were needed
to get it to work for my setup:
211838flag.twbx 441.3 KB