Parkmobile is designed to work in the same way as existing meters, pay stations or payment boxes. Once you have paid in a particular location, you cannot then choose to move your vehicle elsewhere without expecting to pay again for the new location (just as you wouldn't expect a paper ticket to cover your parking in a different area).
If you decide to change location you must activate a new session, as the service is based upon the zone code you originally parked. This rule applies to any location operated by the same parking operator/local authority.