My take is a little different - once a call is owned by the ring group, it stays within the ring group until the ring group has been exhausted. If not, then you could conceivably have a member of the group go on vacation and set their extension to forward to Vmail, which of course might be desirable from an extension need, but a disaster for a ring group. I have the folks within the group set their phone to DND, which effectively is a message to 3CX that the extension is busy. As this is at the phone level, the system will attempt to ring the extensions and you might even get 1 ring or a partial at each as the phone has to inform, but the system will then move on to the next extension until it finds an extension not busy or it then exits the ring group at which point the individual extension settings come into play.
Having said this, I do seem to think I observed a different behavior depending upon the extension number the ring group was assigned. I started with 800 and it seemed like extension settings did impact group handling, but then chaged to 801 and they no longer had an impact. As the latter setting was more to my liking and need, I left it there with the intent of testing to confirm my earlier, but have yet to get around to it as the client where I observed it is some 40 miles away.
If you get the chance, it would be of interest to see/know if indeed there was a difference simply based on the extension number assignment.