Chickens also have a automatic 'nutrition gauge' programed into their DNA. They know when they need more protein, starch, fat, calcium... If there crops are full most of the time it might be because it's hot outside and they've been drinking a lot of H2O to cool down?
One can know that chickens know their own individual nutritional needs because if providing crush Oyster Shell, the hens will pick at it as they please and when they need it.
Chickens will always have a preference for scratch grains, bugs, plants and so on, but if they feel they need more protein, they will go to a layer feed and eat just enough to get by. The hens might not lay as well when fed free-range because they're feeding on other things instead of purely nutrition-packed pellets/mash/crumbles.
My 9 hens and 1 lil Serama Roo free-range... they seem so much happier this way! I free-range for their happiness and pleasure, plus they keep the grubs, bees, grass-hoppers, and flies out of the backyard and stop them from breeding under the rabbit's hutch!
That's always good!
I feed Nutrena CF Layer Feed, Scratch, BOSS, and some value bird seed each day, plus they free range all day. I don't even close them up at night... they roost in my huge Crape Martel bush in the backyard! Never had a problem with predators cause I live in a residential neighborhood in ATL, Ga!! LOL
Hope this helps...