Row total not being calculated correctly in Matrix visualisation [Power BI]

I have the following measures:

StockSales CY = CALCULATE(COUNT('ds SalesRetail'[StockID]),ALLSELECTED('ds SalesRetail'))
Billed Quantity CY = CALCULATE(SUM(AQA0ZSPM________PRICE_REBAT_SQ_View[Billed Quantity]))
Pen. Rate CY = DIVIDE(AQA0ZSPM________PRICE_REBAT_SQ_View[Billed Quantity CY],'ds SalesRetail'[StockSales CY])

I would like my "Row subtotal" to be calculated as follows:
TOTAL Billed Quantity CY/ TOTAL StockSales CY.

However, this is not happening and the Row total is equal to the sum of the percentages above.

What am I doing wrong and how do I fix it?