if you'd want to use a different calculation for the partial sum or sub-totals, use the Dimensionality function. This will give you the flexibility to define what you want to calculate for the totals.
E.g.: I want to calculate the total Quantity for a Region and my first partial sum (on Delete) should show me Average Quantity for that region. But the Final totals should default to total Quantity across all regions.
My expression for QTY2: