There's no change of head pressure when the fuel level reaches the same height as the spray bar.
....3
I did not say that right. The fuel pressure at the pickup is always changing, but it is matched by the pressure reduction of the muffler pressure from the vent. When not centered then the pressure changes when inverted, But only by the small difference in head between the fuel level when upright and inverted. Not a big factor unless off by an inch or more.