New Measure is not summing as expected

New to Power BI so I am having some difficulty figuring this rudimentary problem out. I've got a simple table that contains numerical data reflecting number of staff broken down by employee position by month. I am attempting to create a New Measure to add our "DSP" and "Sr DSP" positions (to create an aggregate count for a line graph), however the measure is not adding correctly. For example, (see reference pic below) I expect the forumla to be returning a total of 204 for row 3 (186+18), when instead it is returning 622. Screenshots include the data table with the SUMX formula and line graph that is currently being spit out with the new measure toggled. 

 Data table

Line graph