Hello Byang,
The name of the topic (the link you have provided) is "Control the Series
Items overlapping via ZIndex property". It describes how to avoid (control) items overlapping, for items in one series. You can not achieve the scenario you describe because the items of one series reside in one panel and the items of another series reside in another panel. The ZIndex is only valid for elements in the same panel.
May be you can use the Opacity of the items instead:
All the best,
Petar Marchev
the Telerik team