Just wondering - does what is selected at sound check in an empty venue get used as-is when the place is full of bodies ?

dedicated high class venues have been using seat material to mimic the absorbancy of the human body for years. Marquees and particularly dance tents offer a whole new dynamic that ensure it will never be perfect.

And the soundman's ears are habituated to what kind of response? Hence the criticism of Rock soundmen. Volume and stability for Rock, balance for Folk.
Even a soundman known for his folk work can (almost always is) too loud for my tastes. Hence I don't pay for concerts and wear earplugs often for dancing.