How to show results only within the selected dates?

[wl2020]

I am trying to create a straight line based on the average value of a selected column. I have the following DAX formula:

IST= CALCULATE(AVERAGE(LN_Dim_Account_Value[value]);LN_Dim_Account_Value[UID]="VHR_12665";DATESBETWEEN(datum_lookup[Name];FIRSTDATE(ALLSELECTED(datum_lookup[Name]));LASTDATE(ALLSELECTED(datum_lookup[Name]))))

Which produced the following result

The value of the line is right, but it is displaying the line from 2011 when the values should only appear between 2018 and 2019. How to I limit it to show results in only the dates I selected? 

[Stachu]

Can you add sample tables (in format that can be copied to PowerBI) from your model with anonymised data? Like this (just copy and paste into the post window).

Column1	Column2
A	1
B	2.5