I’ve never seen more then 92% on my gauge.
I’ve never put more then 90 gallons in, measured with a garden hose flowmeter (2 different types).
Past experience suggests the vent line is not a continuous slope to the tank, may even have dips or loops. May not be vented at the top of the tank, rather on the side.
In the side would put the vent about 1” down from the top.
1” would account for the difference in fill versus rated volume.
2019 DRV MS 39DBRS3