JohnnyG
Weee!
What you get depends on how much charge is left in the battery, the ambient temperature, the temperature of the battery, and if there is another car plugged into the A or B port of your ports number. Max output is only for very low SOC.
One more thing to keep in mind... Those that have been around a while will remember that: Tesla explicitly stated the stations could be throttled, depending on local requirements. This can be caused by many different circumstances (demand, infrastructure limitations, weather, etc), and could last just a moment, or days.... The taper won't be effected; it's driven by how much the battery can accept, not how much the station can deliver.
I honestly don't know how often it occurs, nor how wide spread, but it is a statement of limitation from Tesla about the stations.