Yes, if the system detects that you have approached from the zone 1 side then it will charge the fare to zone 1. However, as with all journeys there has to be a defined fare. There is only one fare for West Ruislip to Notting Hill Gate (not surprising as it’s a direct train). Therefore, if you use OSIs to include zone 1 it won’t make a difference when you touch out at Notting Hill Gate. And yes, via Lancaster Gate would be two journeys.