You could sum N yards into one while keeping a reference area constant...I actually dont know if biodiversity has some characteristic optimal size for a "zone" (obviously an acre of continuous dead wood would not be as effective as much as that acre spread around...).
At the same time...if you have all these indicators in a very small place...that could limit effectiveness, like when you have ecosystem division by roads/walls...
geez, someone was bound to stumble onto something they happened to randomly be doing right...