Drift when restoring window location and size in WPF

I am using the below code to save and restore the position and size of the window on reboot.

I see a 28px upward drift every time I execute this code !

Am I reading the wrong values ​​or am I fixing them incorrectly? Where is the number 28 (chrome size?) Coming from (and how would I account for it programmatically, not a fixed number in the code)?

Here is my code:

public partial class MainStudioWindowControl : RibbonWindow
{
    public MainStudioWindowControl()
    {
        App.MainWindowOwner = this;
        this.Loaded += new System.Windows.RoutedEventHandler(MainStudioWindowControl_Loaded);
    }

    void MainStudioWindowControl_Loaded(object sender, System.Windows.RoutedEventArgs e)
    {
        System.Windows.Window mainWindow = System.Windows.Application.Current.MainWindow;
        mainWindow.WindowStartupLocation = System.Windows.WindowStartupLocation.Manual;
        if (Studio.Properties.Settings.Default.Width > 0)
        {
            mainWindow.Left = Studio.Properties.Settings.Default.Left;
            mainWindow.Top = Studio.Properties.Settings.Default.Top;
            mainWindow.Width = Studio.Properties.Settings.Default.Width;
            mainWindow.Height = Studio.Properties.Settings.Default.Height;
        }
        Debug.WriteLine(string.Format("Loading: Top = {0}", this.Top));
    }

    protected override void OnClosing(System.ComponentModel.CancelEventArgs e)
    {
        base.OnClosing(e);
        System.Windows.Window mainWindow = System.Windows.Application.Current.MainWindow;
        Studio.Properties.Settings.Default.Left = mainWindow.Left;
        Studio.Properties.Settings.Default.Top = mainWindow.Top;
        Studio.Properties.Settings.Default.Width = mainWindow.Width;
        Studio.Properties.Settings.Default.Height = mainWindow.Height;
        Studio.Properties.Settings.Default.Save();
        Debug.WriteLine(string.Format("Saving: Settings.Top = {0}", Studio.Properties.Settings.Default.Top));
    }
}