When the LabelSpot refers to a corner, the Label is actually positioned above or below the subgraph, much like headers or footers in a page layout. Furthermore, when the LabelSpot is TopLeft, if there is a Handle and it is at exactly the same position, the label is shifted right to avoid the overlap. If this node is not IsExpanded, the label is positioned according to the CollapsedLabelSpot. If there is a CollapsedObject the label is positioned relative to that collapsed object; otherwise it is positioned relative to the result of ComputeCollapsedRectangle.

You can override this method to locate the label in customized places. But note that the default behavior of ComputeInsideMarginsSkip is to include the Label in the background/border decoration as computed by ComputeBorder. If you want the label to be positioned outside of the border decoration, you will need to override ComputeInsideMarginsSkip as follows:

            protected override bool ComputeInsideMarginsSkip(GoObject child) {
              if (child == this.Label && this.IsExpanded) return true;
              return base.ComputeInsideMarginsSkip(child);
            }
            

Reference

GoSubGraph Class
GoSubGraph Members