your gallons in the tank can vary also.

example

VW diesel and gas use the same tank system. I did the vent removal on my diesel and gained over 2 gallons of holding capacity.

This extra space is for expansion of gas and the pressure is released during this expansion. When the gas cools down that causes a slight vaccum thus the sucking air in when you remove the cap. Since the gas tanks can hold more you could get some differences but should be minor. Also one or more hybrids use an expanding bladder which can greatly effect readings.

Diesel doesn't expand like gas so the vent mod is safe. I wouldn't recomend it for gassers.