Hi Phaedra,
Where exactly is your coop situated? It might get too hot with the actual temperatures, so the hens will not squeeze side by side like they might do in cooler weather.
I would consider these Omlet coops too small for more than 3 standard size chickens. Do all of your 10 hens sleep...
I don't know if somebody mentioned this to you before, but 3 of your 5 Orpingtons are cockerels.
So this fact might as well be the reason why the lowest on the pecking order is not allowed in at night.