I ran a 2x4 on edge from one wall to the other about 12" out from the nesting boxes. My nest boxes are about 24" above the coop floor. A chicken can not fly into a box. They are birds, they do fly, sorta. Being clumsy fliers they are not concise enough to navigate a flight into a nest box. Place a good landing bar (2 x4 ) 10 to 12 inches out from the nest box. Your hens will fly up onto the bar, walk along the bar examining each box and decide which box is elegant enough to lay an egg in. I use golf balls instead of fake eggs. A chicken isn't that bright, you know. You can play games with them too. Put 3 golf balls into one nest and only 1 in the others. The chickens will lay mostly in the nest with 3 balls in it. Then move the 3 to a different nest and they will lay in that one. Hens are always trying to keep up with the jones' and to lay an egg in a nest box rejected by others would be below their status.
It is also common for new layers to drop an egg anywhere. They don't know just what is happening the first few times they feel the need to pop an egg ( see chickens not to bright above). They will get the idea though. That is the purpose of the fake eggs in the nest. To lure them in. I still end up with an egg on the floor once in a while when the boxes are all occupied and the need hits a hen.