RDPViewer scale size problem

Question

I used RDPViewer in C# (WPF) to display the remote desktop (RDP Session). When the size of the remote screen is smaller than the current screen size, I try to display RDPViewer in full screen, but there will be a gray blank, and the picture will not be enlarged or covered. How should the picture be covered?
this.axRDPViewer.Connect(ConnectString, Environment.UserName, "");
this.axRDPViewer.SmartSizing = true;