dcc.Graph how to adjust height of downloaded image

Hello. I’m using the following layout code for a figure:

html.Div([html.H3('Simulation Results'),
                                        config = {
                                            'toImageButtonOptions': {
                                                'height': vheight,
                                                'width': 1600,
                                                'scale': 2}})]),

I am wondering how to change the vheight variable either within the @app.callback or as a user dcc.Input. Any sample code to show how this can be done would be very much appreciated.