I wouldn't waste that much space in a small coop for that many next boxes. For no more than the number of hens that can fit in there, I'd just put ONE in. MAYBE two... or one that's two boxes wide but not divided.
I have 21 birds (20 hens/pullets). Not all are laying yet... about half. I have on larger community nest box... it's basically 3 boxes without dividers. Most of my laying birds use one particular spot in the community box, but on the occasion two are in there at once, they have a little more room. If there's no waiting... they pretty much ALL want the same spot.
I've seen two or three hens pile into ONE 12" next box to lay at the same time when there were other nests available. They don't have problems sharing.
If there's another hen's egg in the box, they don't care, they lay and leave their egg with it. In fact, times when an egg gets laid in a different spot, the next hen in tends to roll the wayward egg back into the favored spot.
Other times, like other posters said... they will literally wait in line for the preferred spot rather than use an open nest that's NOT the preferred spot.
I REALLY, REALLY wouldn't use up so much room in your small coop for that many nests. You'll be kicking yourself when the birds pick *one* spot and all the other space goes unused.
And whoever made the 'rule' about one nest box per 4 hens... I swear they never had chickens...
One... or two... MAX... or at the VERY least, make them all removable so when you see that they are just taking up space, you can easily yank them out!