Chickens???

Right now we have 13 hens that are laying, we have 4 nest boxes and they all insist on using the same box.  There have been many times that 2 are in it at the same time and one or more might be waiting to use it.  The nest boxes are all the same size, have the same nesting material and are all next to each other.  It will be interesting to see what nests the 12 pullets that should start laying in August will choose.  We plan on adding 2 more nest boxes before then but with the 13 just using one, sometimes two nest boxes do we really need to?  Crazy chickens!!!!