I am looking for the definition of a flatness measure in lattice theory.

More generally, I am looking at finite-height lattices and I want to measure their complexity, with a perfectly flat lattice having the lowest complexity, and the highest complexity being open to the author's definition.

A perfectly flat lattice would have all (non-top, non-bottom) vertices connected only with both top and bottom and show the lowest complexity.

Despite my best efforts, I have no found such a measure. Is it known by another name?