Our 26 Buff Oprington Chicks are now 2 1/2 weeks old. I built a set of six nesting boxes on legs. I want them to have enough clearance from the floor so that the adults can use this area for feeding and watering. How high should they be? I see a lot of articles that say 18 inches but is that for average chickens? BO's are going to get larger than average. Do I need to go taller? I still want the to to be less than 48" and that would give me about 20" clearance under. Is that enough?