Here's the part I'm getting at. Let's say someone has a 70A main breaker for the total service of the entire house. You have been saying that if the wall connector is set to something like 20A internally, then it doesn't matter how big the breaker is--go ahead and put it on a 125A circuit breaker, even though the entire feed for the house is only 70A, and a load calculation would never allow a 125A circuit in there. You are saying the switch inside the wall connector of 20A is all that matters with respect to complying with the load calculation. I don't think that would be the case.
For my code reference, I don't know if I can locate this exactly, but it should follow the same "spirit of the law" as the NEC requirement that the rating of an outlet must be at least as high as the circuit breaker it is on. So you can't put a 6-50 outlet on a 70 or 80 or 100A breaker. I would think that same rule applies. NEC wants the breaker to cut off early, so it shouldn't have the breaker much higher than the device.
To clarify, I do not think I have suggested that someone install a branch circuit (for an EVSE) with a breaker that is larger than their overall service feed rating. While off the top of my head I don't know where in the code that this is banned, but it is not very intuitive. There would really never be a use case for doing this unless you were planning to upgrade the service/feeder soon that was the limiting factor.
I *have* however suggested that folks put a ridiculously large breaker (say 50a) on a new branch circuit (along with appropriately rated wire) for a Wall Connector even when lets say they only had a 70a main service feed. While you would never be allowed to operate it at 50a due to load calculations limiting you, it would be ready in case you upgraded that service to 100a or 125a, etc... Really the key is that I have in some cases recommended that folks wire the Wall Connector with wire and a breaker larger than the load calculations would allow today so that they have the flexibility to change its settings as factors change. Examples would be: 1. They convert their oven, range, furnace, water heater, or dryer to gas which frees up load capacity that could be re-allocated to the Wall Connector. 2. They upgrade the main service/feeder as mentioned. 3. Or, really the kicker is this one: 220.87 says you can throw out all the code calculations and look at *actual* load over the course of the year and use that to base your demands on. It is my belief that something like the "sense energy monitor" could allow you to make an argument that the mathematic load calculations were not representative and that you should be allowed to turn up your Wall Connector higher than the calcs would otherwise allow. If you did not pre-wire and pre-install a larger breaker to allow this, it would be a ton of expense to later increase capacity.
I also need to clarify that I have never suggested to put a Tesla Wall Connector on a circuit greater than 100a (and I never would) since this is what the unit is rated to. Specifically, the nameplate on the side of the unit says it takes 80a of input, but since it is a continuous load we have to provide wire of 100a ampacity along with the matching circuit breaker. The install instructions say to install it on a 100a circuit (or lower if you can't support 100a).
But to the meat of your question:
Load calculations of Branch Circuits, Feeders (subpanels), and Services are covered in Article 220. These are completely decoupled from "Overcurrent Protection" which is covered in Article 240. The size of the breaker has nothing to do with how we calculate load. They are separable concerns.
Article 220 is quite complex and it is unfortunate that it does not address EVSE's directly (even though it seems to have special language for just about everything else). From what I can tell, EVSE's fall under 220.14(A). (also note that Article 625 which covers EV charging says nothing about load calculations there)
So to me, this covers a NEMA 14-50 for EV charging with a UMC, or a hardwired Wall Connector.
I read that as a UMC Gen 1 is calculated as 40a, times 1.25 due to continuous load, so 50a. A UMC Gen 2 would be 32a times 1.25 so 40a. In both cases it would be on a 14-50, but for the UMC Gen 1 you would only be allowed to use it on a 50a rated circuit. A UMC Gen 2 would be allowed on either a 40a or a 50a rated circuit (still on the 14-50 receptacle).
But to finally answer your concern:
I calculate the "load" of a Wall Connector based on what the rotary dial is set to. The only other option would be to do it based on the max nameplate value listed on the side of the device which is 80a (100a when factoring in continuous load). If you used that number basically nobody would be allowed to install a Wall Connector as it would fail load calculations.
Something that is interesting here is that unlike a motor where you can configure different tap points that might cause different loads, in the case of the EVSE you are having the EVSE send a signal to the car and then you are *trusting* that the car does not draw more than you told it that it is allowed to. The actual device doing the restriction is not the Wall Connector. Now it begs the question in say commercial EVSE's: Do they have current CT's and can they detect how much a car is actually drawing and cut it off if it breaks the "rules" (instructions) the EVSE gives it?
So assuming we can get on the same page about the rotary dial being the "nameplate value" of the load being served, the other question is one of overcurrent protection:
The Wall Connector is rated for up to a 100a circuit - its components and the wire to the vehicle (and presumably the vehicle itself) are all rated so that if there is a fault (short), enough current can flow in order to trip the 100a breaker. The danger would be if the Wall Connector had thin wires in it that might melt and catch fire before flowing enough current to trip the main breaker. But this is not the case since it is rated up to 80/100a.
Now of course you absolutely need to protect the wire from the breaker panel to the Wall Connector, so to do what I suggest of say installing a 50a circuit even if you crank the wall connector down to 24/30 amps, you would need to install at least 6 AWG copper NM cable as an example to match or exceed the 50a breaker rating.
Does that make sense? I think what I have been recommending is both safe and within NEC regulations (and provides the user future flexibility and investment protection if applied in the right situations).