How to detect offline status?

I've got a webhook subscription that is listening for account presence events. When I shut down RingCentral, I had expected to receive an event with presenceStatus or userStatus set to offline. However, this is not the case. I've also tried calling Get User Presence Status but this returns an available status. Calling Get Unified Presence does return offline but I would prefer to use webhooks. When I shut down the app my presence in RingCentral is displayed as offline so why doesn't the webhook report this?