Thanks for chiming in!
I appreciate the graph, and it makes sense. At least for me, the disconnect occurs when I try to correlate SMT with the 'miles remaining' meter on the car's display. E.g, my Model 3 LR has a rated miles consumption of 237 Wh/mile hardwired. When I charge to full I see 308 miles of range which corresponds to 308*0.237 = 73 kWh **
So when the car is fully charged, the buffer is included in the rated miles calculation
Once I have depleted the battery charge to 0 rated miles remaining, a buffer of 73*0.045/0.237 miles remain in the battery that are usable (with the caveats you mentioned.)
I realize that your are not responsible for Tesla. Perhaps the confusion here is that 'usable' in SMT is not always the same as 'rated miles' on the screen display.
**Yes, you used my car for your graph example