Get position of Rect in Rect in EditorWindow

I have a problem getting the position of a Rect inside my EditorWindow:

I'm working on a node based editor, so in a new EditorWindow I create a node with myWindow = GUILayout.Window(windowID, myWindow, DrawNodeWindow, myName);

and the setup for the node is in here (minimal example)

 void DrawNodeWindow(int id)
 {
      //some Layout stuff
     if (GUILayout.Button("", EditorStyles.radioButton, GUILayout.Width(16), GUILayout.Height(16)))
     {
         //draw a line beginning in the center of this button
         Rect myRect = GUILayoutUtility.GetLastRect();
     }
     //More layout stuff
  }

Now I want to draw a line from one nodeWindow to an other. For this I need the center of the radioButton I created.

So I get the Rect of the button with GetLastRect(). I already checked if I got this right by using EditorGUI.DrawRect(myRect, color.black) and there is a black Rect over my button, just where I need it.

Now I can't get the position of myRect.

MyRect.position is somehow always 0,0. It seems I would need to add the position of all the other Rects it is in to it (like the position of the window for example) but the problem is I use lots of autolayout stuff like Beginhorizontal nested in a BeginVertikal and so on. So I don't really know how many Rects there are.

I simply need the position of the Rect in my EditorWindow.