[Slump Tester]

"...add to the equation that the aircraft over water is in a higher humidity environment which in turn further decrease the density of the air..."

Higher humidity would INCREASE the density of the air, wouldn't it?

[HiTech RedNeck]

H2O molecules are not as heavy as N2 or O2 molecules, however air at normal climatic temperatures and pressures also can’t hold a very large proportion of water vapor so it can not affect overall air density very much. Condensation of water on cooler surfaces might interfere with their aerodynamics.