public virtual void LayoutHandle()

public override void LayoutHandle() {
  if (!this.IsExpanded) return;
  GoSubGraphHandle h = this.Handle;
  if (h != null) {
    RectangleF b = ComputeBorder();
    // top-left, in the margins
    h.Position = new PointF(b.X, b.Y);
  }
}

// To place the handle at the top-right corner, you could implement these overrides:
public override void LayoutHandle() {
  if (!this.IsExpanded) return;
  GoSubGraphHandle h = this.Handle;
  if (h != null) {
    RectangleF b = ComputeInsideMargins(null);
    // top-right, inside margin
    h.SetSpotLocation(TopRight, GetRectangleSpotLocation(b, TopRight));
  }
}
            
// Make sure the collapsed subgraph body (including any CollapsedObject)
// is positioned to the left of the handle.
protected override RectangleF ComputeCollapsedRectangle(SizeF s) {
  PointF hpos = ComputeReferencePoint();
  return new RectangleF(hpos.X + this.Handle.Width - s.Width, hpos.Y, s.Width, s.Height);
}