Minimum value between two summed values / measures

Hi All,

I'm trying to get the minimum value of two summed values, or measures (whichever is easier!). 

I have a table visualisation at the moment which shows various fields across multiple tables, and I have a field for 'Receipt Quantity' from the table RCT-PO, and a field for 'Sold Quantity' from the table ISS-SO. On my table at the moment, these values are summed as it's multiple rows that are just summarised on the table.

What I'd like to do is have a measure that gives me the smallest value between the total of Receipt Quantity and Sold Quantity based on the filters applied in the report.

Can someone assist? I've managed to do a MINX with UNION, but this brings back the smallest single value (i.e. one row), not the sum of all the rows for this value. 

Many thanks,

Dayna