I always try to have a nice warm spot and then cooler areas. They generally do what's best for themselves. Pasty butt often comes from the chicks getting too cold during shipping.I've found that if I keep the chicks too warm and too dry, that's when they get pasty butt. I know conventional wisdom says to start them out at 90°F for the first week and lower it 5° each week, but ours do best at about 85° in the brooder in a 70° room, with a humidifier on. Our last three batches of chicks have done very well this way, and we've had almost no PB; our last batch had only one chick with one episode. The chicks keep each other warm by huddling occasionally, otherwise they are active for the most part.