I know 12X12 is recommended, but I always here of the "favorite" nesting box. How big is your chickens "favorite" box? Also what size is your chicken!
I'm not sure is the issue in this instance - hens just seem to prefer one or two nest boxes. It's possibly more of an issue of privacy or downright stubbornness! Ct
All my nests are at least 14" wide x 14" deep x 16" tall with a 10" diameter entrance for coziness and good looks. Nice and roomy for turning around to get comfy. They still can have a favorite, it's just how they do. But I've found that keeping one or two fake eggs/golf balls in all the nests helps spread the love, tho they still can bicker over or wait for a favorite, the 'favorite' can to change day to day or week to week.