You might want to read the second to last update at end, before hearing this story.
So I am on the phone with Tesla Roadside Assistance and what the rep is saying is blowing my mind. He has indicated that the third paragraph at
https://www.tesla.com/support/charging/supercharger/idle-fee, specifically:
"Idle fees only apply when a Supercharger station is at 50% capacity or more. Idle fees double when the station is at 100% capacity,"
is indicating that at some superchargers they can charge you an idle fee that is a percentage of what you charge even if you have lifetime free supercharging AND you do not leave the car idle without charging (in other words, even if you disconnect before it has finished charging. In addition he is telling me that although a supercharger may indicate 80% max charge and you can change that, some superchargers may stop charging at a different level such as 95% even though you got the warning that for 80%. Also, my saying that I wasn't notified of either the fee for just using a supercharger that is labeled as "idle fee" nor the supercharging stopping at.
Update: Then he came back on the phone and apologized for being incorrect and said I was correct in everything I explained to him. Still no explanation of why my car stopped charging at 96% even though I had it set to 100% (I changed to this after the initial 80% change warning).
Update 2: Was told the explanation of why even though I disconnected immediately after seeing a notification on my phone that the charging had stopped, that may have been after the grace period due to the notification not being received by my phone for over five minutes (notification delay).
This is my second idle fee I had waived and I believe neither situation was my fault (the other was a super charger charging my car while simultaneously charging me an idle fee for 39 minutes).
I now have a service call scheduled to find out why my car stopped charging at 96% as there may be an issue with the battery or calibration.
One other thing they made clear, when you go over the grace period of five minutes, you are charged the excess minutes over five AND the five minutes for the grace period. So if you disconnect from the charger after six minutes after your charging stops, you get charged for six minutes of idle time (not one).