If it is measuring Ah from/to the battery, it has no good way of knowing where "zero" is without discharging the battery "completely".
Also, the top 8% of the Amp-hours should give us more energy (more miles actually driven) rather than less energy and less miles driven.
Many experience getting only 50 to 60% of the miles from the Top Bar, compared to the middle bars, even when starting near 278 (to 280) raw.
But, anything is possible.
No matter how this is derived (probably in the BMS), it performs the function of a fuel gauge, with an uncertain (variable) low end.
It appears that another mechanism, like lowest (or highest) cell voltage, is actually telling the car to STOP driving (or charging).
We think we have found battery voltage and current elsewhere.
See SOC/GID-Meter and CAN-Do Info
2011 LEAF, 2014 Tesla S85
2018 & 2019 Tesla Model 3
Solar PV: 33 x 225W -> 7 kW max AC
Craigslist: Xm5000Li Electric Motorcycle