Its kind of a loaded question because it really boils down to conceptual design rather than sticking to strict generic wall heights. The footprints for all of our structures and tiles fall into the WorldWorks standard of 7"X7" and the general scale is suited to all 25-28mm miniatures.

The building types and genres (or time periods) are distinctly different. Mars Station conceptually is a futuristic version of an old-west settlement. The buildings are intentionally made to look utilitarian and sort of "squat". The idea being that most of what has been constructed there had to be shipped from off planet and therefor packed in the most efficient way possible. Compare that to Urban Mayhem and your dealing with a normal city environment where wall height and other elements are not constricted by the environment or construction methods.

All of the sets "work together" in terms of general scale but the wall heights may differ a little depending on which set you're dealing with and the environment it's representing.