Leadsled, I understand your explanation, but the proposed regulation 91.510 does not say anything about 'order of accuracy'., it doesn't explain anything. (and interpreting the fuel gauges in a lot of GA aircraft would be more like 10% accuracy rather that your 3% in an RPT A/C)
91.510 bluntly states that you must have your (ill-defined) fixed-reserve intact when you land, otherwise you are guilty.
There is no provision for any defence.,
It doesn't care if the actual winds are worst than forecast.,
It doesn't care it you have a slow fuel-leak.,
It doesn't care if you get held by ATC because of problems due Wx or worst-than-usual congestion.
It doesn't care that you've had to do bigger diversions due to worst-than-forecast Wx or conditions.