how to combine 12 month rolling averages with monthly data on a single chart

[#1]

I havea  chart that plots 12 month rolling average performance data for mutiple plants plotted over time and would like to add a target line to the chart

I am using the "asof" table method to generate the moving averages as per Calculating rolling n-period totals, averages or other aggregations by G Wassenaar.

When I add an expression for the traget, the individual plot lines for each plant get combined to one plot line, plotted against the target line

How do I retain the individual plot lines with teh target line?

Thanks in advance

Stephen