Great question. From my perspective, you’re trying to determine the percentage that each customer represents out of the total amount from all customers.
I am using a similar example in a report I created of Account Receivables data. The use case should be the same but in my case I am showing the percentage of a customers Outstanding Balance (Open Amount) related to the Outstanding Balance of all Customers.
To set up this up, you can create a new Calculated Column that contains an expression of the:
Amount Open / Aggregated Total over All customers.
In the example below, you can see how I defined the Aggregation to be performed over the Amount Open field with “Total” operation.
Once you have the calculation defined you just need to add the calculated column to the Aggregated Values section of the IR so that the Totals are calculated on the Customers Row Group.