Hi @misamc24 , great question thanks for asking it here in the community. The Fuel tank capacity setting is used for more than monitoring fuel transactions: it can help MyGeotab calculate the volume added for a detected fill-up when the vehicle reports fuel level as a percentage. If the vehicle reports fuel volume directly, that percentage-to-volume calculation isn't needed.
Entering the correct capacity can therefore improve fill-up volume reporting. For vehicles with multiple tanks, enter their combined capacity. A manually entered value takes priority over an engine-reported or estimated capacity. The setting does not change the raw fuel-level reading reported by the vehicle.
The Fuel and Energy Usage report documentation (https://support.geotab.com/help/mygeotab/reports/sustainability-reports/fuel-and-energy-usage-reports) describes fuel usage in terms of engine-reported fuel used, imported transactions, and distance. I couldn't find another documented use of the asset setting beyond capacity determination and fill-up reporting.
Hope that helps!
Eishi FUN