Irrigation - Project Boundary

Hi, I am working on a building located in a development in a business park with 4 buildings. The site has a large non-symmetrical vegetated area in the middle which is shared by the four buildings. Since this is a Commercial Interiors assessment and this is the only credit affected by this situation, undertaking a campus approach does not seem the best option. Would it be acceptable if I make the calculations for the whole area? Since results are a % they should not be affected by the extension of the area included. Your feedback would be much appreciated. Many thanks Regards Alicia