The setting in the backend doesn't affect the map of a particular event. That setting is ONLY for the all events map (the one which is on a separate page).

The zoom level of a particular event is being saved to a DB whenever you're updating the event's location manually via putting or dragging the event's marker. So the only known way of setting the zoom like on your screenshot is to zoom out completely and put/drag the event's marker thus updating its location along with its zoom state. If you want to zoom in and keep that zoom state then you must drag the marker a bit for this to be saved into DB.