172 driver,
Is not fuel burn a derivative of fuel flow, eg...400kg/h? In all my years I have never heard of fuel burn being "measured near the nozzles in the engine". Could you please elaborate.
Also, I would suggest that the "slight increase" in fuel quantity after shutdown is due to the fuel settling after sloshing around in the tanks due to landing/taxiing and not "fuel pouring back" due to the tank boost pump non return check valves.