I have a dozen shipped eggs going in my incubator. 8 of them seem to be developing, but about half of them are developing right on the end of the egg where the air sac should be. I am incubating these in an egg carton. It is the first time I have incubated in a carton. Is it normal for the chick to delvelop like that when incubating in a carton? They are only on day 6. Thanks