I have published a map image from Pro, containing a layer with a mimimum scale set to 1:205,000. Turns out I want to have it visible regardless of the scale. I have added the map image to a map in Portal. Neither from the 'change style' dialogue in the map or 'Set visible range' from the layer menu can I over ride the minimum scale set at time of publishing the map image. I also checked the JSON for both the Portal map and the map image using ArcGIS Online Assistant and couldn't find any minimum scale settings to modify.
I am now republishing the map image with the required scale settings. Please advise if this is the only way.