Dax Measure for selecting a value in a specific column based on dates

Hello, 

I'm having problems wrinting a measure in dax. I have a fact table "EmployeeMD" that has all the employees and the working positions that they now have or had in the past. Every position has a start and end date and the first startdate and the last enddate are also grouped to make the "from - to" date that the employee is active. If the employee is still working, the enddate = 31/12/9999. Every position has a FTE value that may or may not change. 
For example Employee X has 5 different positions (rows) in the table. The "from-to" is the same for every line. The FTE value changes over time. The position start and enddate give the periode the person was active on that position. 

I also have a dates table with dates ranging from 01/01/2020 untill 31/12/2023.
The data is visible in the following matrix:


This is the measure I currently have:

FTECount =

Var FTEstartdate = MIN(EmployeeMD[PositionStartdate])

Var FTEenddate = MAX(EmployeeMD[PositionEnddate])

Var MaxDate = MAX(Dates[Date])

Var DateFilter = FILTER(EmployeeMD, FTEstartdate < MaxDate && EOMONTH(FTEenddate, 0) >= MaxDate)

Var FTEbyposition = CALCULATE(SUM(EmployeeMD[FTE]), DateFilter)

return

FTEbyposition

This measure works on the lowest level and looks in what period of a position the month and year is and takes the sum of the FTE values that corresponds. But when I collapse the matrix, the sum of all the 5 FTE values is made, resulting in:

I figured this is because the dates on this level that are used in the calculation are the "from to" dates and every line in the table is in this range, resulting in the sum of all FTE values. 
How can I rewrite the measure to have the count of a single fte value that corresponds with the month and year when the matrix is collapsed? 
Thanks in advance!