However, doing so will mean that the Overview Diagram will not automatically zoom the Diagram.scale to show the whole Diagram.documentBounds of the observed diagram.
I haven’t tried this, but you could implement a “DocumentBoundsChanged” DiagramEvent listener on the observed diagram to call Diagram.zoomToFit on the overview. That way as the document changes size the overview will be zoomed normally, but you will be able to zoom in and out in the overview.