Consider a very long vertical cylinder containing air in thermodynamic equilibrium. Observe that the air column is necessarily bottom heavy. The macrostate is described in part by a pressure gradient that is due to gravity. All corresponding microstates for this particular macrostate will have a matching density distribution. It seems that a top heavy distribution of the air molecules is not a valid microstate of that macrostate. And neither is a uniform density distribution along the cylinder length. When gravity is reversed, the density distribution also reverses.
When the gravity force is removed or equalized along the cylinder's length by turning it horizontal, it seems the density distribution necessarily becomes uniform in equilibrium. A microstate where all the air molecules are concentrated in one area appears to not be a valid microstate of that macrostate because the density gradient causes a pressure gradient (all else equal) that is different than the uniform pressure of the uniform density system, hence the two macrostates are not identical.
Can we therefore say that entropy forbids density fluctuations in a gas-filled system in thermodynamic equilibrium? In other words, can we say that the only valid microstates of a particular macrostate are those that always match the macrostate parameters?