Can you add a dynamic variance in SAC Analytical Application

I built an application within the Analytical Application Designer.

We have a chart with only one keyfigure. The keyfigure which defines the output of the chart is selected via a radio button. The options within the radio button group are YTD (year to date) and MTD (month to date).
So our chart either shows YTD or MTD. We compare these values to those of the same period of the previous year and want to visualize these via a variance.

Our problem is, we can't manage to implement this via the Analytical Application Designer. We can define the variance in the chart options but only for one keyfigure. We can't set it up, so it changes dynamically, depending on which keyfigure the chart uses.

Thanks in regard,
Ömer.