The topography of the zoning and building layout matter. Consider two neighborhoods which are 2-mile squares in shape. One neighborhood has a commercial district in a single corner, the other neighborhood has two such districts at opposite corners of its square. The second neighborhood may score twice as walkable, but what matters to the home's individual walkableness is how close it sits to one of those districts, since you presumably want to walk to the store and to an office in a corner that has a commercial district.
Choose a place you would like to walk, shop and work, then find a home located within a walking distance from those places, and you may have MANY good options, more than your zone-based averaging will reveal.