protected Point OverlayControlPositionRatio {get; set;}

public ProSnippetMapTool()
{
  //Set the MapTool base class' OverlayControlID to the DAML id of your embeddable control in the constructor
  OverlayControlID = "ProAppModule1_EmbeddableControl1";
}

// Override the MapTool base class' OverlayControlPositionRatio property to set the position of the embeddable control
protected static void OnToolMouseDown(MapViewMouseButtonEventArgs e)
{
  if (e.ChangedButton == MouseButton.Left)
    e.Handled = true;
}

// Override the MapTool base class' HandleMouseDownAsync method to set the position of the embeddable control
protected static Task HandleMouseDownAsync(MapViewMouseButtonEventArgs e)
{
  return QueuedTask.Run(() =>
  {
    Point
          //assign the screen coordinate clicked point to the MapTool base class' OverlayControlLocation property.
          OverlayControlPositionRatio = e.ClientPoint;
  });
}