RankX to only a certain level

Hello! I am using RankX to determine my top customers. That formula is working really well for some applications, but poorly for others.

For instance, I have a matrix with some information about the customers and then these figures split out beneath by brand. I then want to set the table to only show the top 15 customers, by using a Top N filter on the ranks.

This method works well whent the brands aren't shown beneath. However, with the brands in the table, it is showing more items than planned because it's also giving rankings at brand level. How can I get RankX to only give me one value - a ranking at the customer level?

Right now my code is as follows, where a "Chain Parent" is a customer. adding filters on all brands don't seem to fix it.

I am Live Connected to Analysis Services, so I am running into the issue that I can't add calculated columns, unfortunately.

Thank you in advance!

Hannah