Theory
The only explanation to it after monitoring for a long time is that it isn't about what reads the fuel it is about how it is read and measured by the corresponding capcitators , so just consider the body angle and the attitude with the existing CG and what phase of flight you are in? And you will figure out why with more nose up attitudes you get more fuel indicated and vice versa , effect of center tank fuel consumption on the above factors and why we have more fuel indicated by the begining of the flight and less than what was indicated by it's end .