Find my approach as reference below and stored in attached workbook version 10.3 located in the original thread.
1. M1. Rank: RANK_UNIQUE(sum([Quantity]))
2. Drag the required objects to the indicated locations. Set M1. Rank to Discrete and Compute Using > Table (down) and filter on <=10
parameters_nalmai_10.3.twbx 360.0 KB
So we can do this using the Top N filter on Customer Name...in the filter options
Now the issue is that this "Top N" is computed before any filters are applied, but we can get round this by adding the filters to "context"
Hope that helps
parameters - SR.twbx 360.6 KB
Thankyou so much
Its working as expected