You could use the UXWindow WindowStateChanged event handler to modify the width and height after yje UXWindow is maximized. Here is the snippet:

private void wndHome_WindowStateChanged(object sender, WindowOperationEventArgs e)
{
    UXWindow wndObj = (UXWindow)e.OriginalSource;
    if (wndObj.WindowState == Intersoft.Client.UI.Aqua.UXDesktop.WindowState.Maximized)
    {
        wndObj.Height = this.ActualHeight;
        wndObj.Width = this.ActualWidth;
    }
}

FYI, we implement the maximize behavior bacause by extending the UXWindow to its full size, it will block user from using the UXWindow element located below the UXDesktopDock.