A lot depends on what you want them to do in the nest box.
They don't need 'privacy'... that's a human thing.....they do need to feel 'safe' tho.
Chickens will choose the spot to lay their eggs. If they don't like your "nesting boxes" they won't use them. I agree with @aart that they don't need privacy, they just was to feel comfortable and safe. I leave my coop door open, so my girls get no privacy but they seem to love the boxes!
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