FirstSortedValue from an Aggr Measure

[CC_Abbott]

Hello,

I have the following data in Qlik Sense.

Dimension	Measures
Entry Month\Year	Rate	Sales Qty	Count
Jan-2019	0.00108041	41692	45
Feb-2019	0.001354416	27586	55
Mar-2019	0.001140416	45236	29
Apr-2019	0.00110921	56928	59
May-2019	0.001060559	40125	38
Jun-2019	0.001054936	35515	37
Jul-2019	0.000986442	37502	31

I'm attempting to retrieve the last months Sales Qty.  To retrieve the last month I used the following expression:

=FirstSortedValue([MonthYear],-aggr(Distinct([MonthYear]),[MonthYear],[Year]),1)

However, I'm not able to use the same expression and substitute for my Sales Qty when I use the following:

=FirstSortedValue([Sales Qty],-aggr(Sum([Sales Qty]),[MonthYear],[Year]),1) 

The above return a number 5, which does not align with any of my data sets.  I have 7 months in my data and Sales are in the thousands.

I typically use Sales Qty from a known variable v_Sales.Qty or from a variable with a set of data, so I've tried:

=FirstSortedValue([Sales Qty],-Aggr( Sum( {< $(v.ControlPeriod.Rate.Set) >} [Sales Qty]), [MonthYear],[Year]),1 )

or

=FirstSortedValue( {< $(v.ControlPeriod.Rate.Set) >}
Aggr( Sum( {< $(v.ControlPeriod.Rate.Set) >} [Sales Qty])
, MonthYear),1 )

What am I doing wrong here or does FirstSortedValue not appropriate for Measures?

My experience with set analysis and expression coding is limited.  Any help would be appreciated.

[CC_Abbott]

Yes, in order for the expression to work I have to label the measure as Moving Avg.