Hmmm,
Don't forget temperature effects - DFC alluded to it by referring to "under ISA", but no harm to explicitly state that
Moist Air Less Dense than Dry Air
at the same temperature.
Cold, moist air can be more dense than hot, dry air. This is how water injection of turbojets works, by spraying cold water into the compressed air to cool it and increase its density, therefore allowing a greater fuel burn and resultant thrust.
SD