KPI Show average as target

Hello,

I have a problem using KPI. I use time series data and get new values from the server every 5 minutes. The KPI shows the most recent value and a trend line of a filtered time period. Now I want to add the average value of the filtered period as target value. I built my time period filter in the way explained in the following video: 
https://www.youtube.com/watch?v=Xi86HHEaY_M

The best I could achieve so far was that the overall average is shown as target but not dependent on the filtered period. Do you have an idea how I could fix this?

Best,
Hannes