C# How to place a window between desktop backgrounds and desktop icons

Question

I'm trying to make a program like a desktop calendar,finding problems when trying to place the window into desktop. I called windows API, it did put the window into desktop, and win+D won't hide the window, but still, the window remained above desktop icons, My code was like

var handle = new WindowInteropHelper(Application.Current.MainWindow).Handle;
            IntPtr hprog = FindWindowEx(
                FindWindowEx(
                    FindWindow("Progman", "Program Manager"),
                    IntPtr.Zero, "SHELLDLL_DefView", null
                ),
                IntPtr.Zero, "SysListView32", null
            );
            SetParent(handle, hprog);

Is there a way to put the window below those icons?