Pretty Graph Time!
This should be fairly self-explanatory, but I'll try to explain anyway. For the 90kwh batteries, this is what is going on behind the scenes: The car starts out reporting to the driver that it can travel XXX miles on it's current charge of 100%. It gets this number by assuming that it can use the Nominal Pack capacity to do XXX range. But we all know that the number used for Nominal includes the 4kwh brick protection and can't be used for driving. So the car has another number, Usable Capacity, which has that 4kwh subtracted. This is supported by the fact that 0% on your dash corresponds with Usable Capacity in the BMS also being 0%.
At some point below 90% and ~80% (closer to 80), something magical happens. The car stops using Nominal Capacity to calculate range remaining, and instead uses a number between Nominal and Usable. That is, until it gets down to 20%, by which time, it's only using Usable. Notice how the the distance between the two lines gradually, and linearly, gets closer together as SOC drops.
View attachment 317809
It might be tough to see since I shrunk the data-set down for ease of use, but refer to the rate in change on the small graph; the lines are flat between 100 and ~80, and also between 20 and 0.
View attachment 317813
I'm going to continue to make bold statements and say that Tesla knows about this huge "What's your 90%?" thread and that is why their magic only starts to happen below 90%. They want their best foot forward so-to-speak, so as not to raise concerns from 90kwh battery owners that their range has degraded so severely.