SUMPRODUCT in Matrix Visual

HI,

I have a relatively simple dataset copied below where I am seeking to replicate SUMPRODUCT from Excel by working out the difference between sub asset classes between two dates and applying a weighting. I have been able to create the measure but it is displaying oddly in the Matrix visual in Power BI desktop so I am hoping someone can point me in the direction of what I need to add:

The table is called "Benchmark Performance (GBP)" and I have been able to create a measure as follows:

Value % difference from Period Start GBP =

VAR STARTVALUE = CALCULATE(SUM('Benchmark Performance (GBP)'[Value]), 'Date'[Variable Date] IN { "Period Start" })

VAR ENDVALUE = CALCULATE(SUM('Benchmark Performance (GBP)'[Value]),'Date'[Variable Date] IN { "Period End" })

VAR BBPERF = DIVIDE(ENDVALUE-STARTVALUE,STARTVALUE)

VAR RESULT = SUMX('Benchmark Performance (GBP)','Benchmark Performance (GBP)'[Weight]*BBPERF)

    RETURN

RESULT

 

This is returning what I'd expect at Sub Asset Allocation level (SUB AA) in a visual but the wrong weighting for BB Summary level:

 

In the above example, I would expect the output to be Gilts 0.18+0.17% = 0.35%

 

Any pointers greatly appreciated