Filtering to remove summary task information

Hi,

I'm fairly new to Project Online and the use of power view and I'm creating a graph/table that provides the sum of the forecast cost each month so we can project cash flow.

I have a query pulling the TaskTimephasedDataSet and I'm using SUMX to total the data. That was the easy bit. The problem I have however is that the query includes the summary tasks and it appears that the flag TaskIsSummary is located in a different Tasks table. I can't seem to work out how to filter the TaskTimephasedDataSet to remove the summary task information so my monthly cost forecast is correct.

Any thoughts or pointers would be greatly appreciated!

Thank you
Conrad