Well, the P/A ratio works really well in many cases. <0.15 ratio using -3 foot distance threshold and >.02 ratio using -6 foot distance threshold results in a reasonable number of selected grid cells. However, in this particular case in the photo below, the opposite is true. These rooms have a very low P/A ratio, but using -3 feet results in too many grid squares being selected (in this case 27). Using -6 feet is more reasonable (20 grid cells selected), but that blows up the model. We want to count grid cells inside the room, but using 'within' or 'completely within' also results in far too few grid cells being selected.