Are your chickens acting stressed? It is amazing how the right number in the set up, will get along just fine, and one or two more head, will add the stress level, to the point you can feel it.
While the numbers are a guideline, you can cheat..... at times. As you have noticed, chicks take up little room, but full grown hens take up a lot more. During the summer, when the birds are mostly outside, for most of the hours of the day..... you can also, have a few more in there. However, going into winter, when the girls will spend hours more on the roost, due to the short days and long nights, you need to get much closer to the ideal number.
so, as we are going into summer..... I don't think it will be much of an issue until fall.