Just guessing here, would it make more sense to base yearly maintenance on $/sq ft instead of overall property value? Would better take in to account expensive but modest (lower maintenance cost) versus huge home (higher maintenance cost).
$/sqft glosses over local labor costs, level of finish, landscaping, etc., which is why you see people suggesting 1-2% of value per year, though you're right that it would be an improvement to separate out the value of labor/materials from the value of a the bare lot.
