How to filter a Time Intelligence Function

My issue is, I have a matrix visual with two columns. The first column is a simple sum that returns either a number or a blank depending on the slicer settings.  The second column is a time intelligence function showing the change from last month, which returns a number for each row.

What I want is for the second column (change from previous month) to only return a value when there is a value present in the first column, (Otherwise return blank). What is partly tripping me up is that the previous month function needs access to 'old' data, so I cannot just filter to current conditions as these conditions will not be accurate to last month also.