I have heavy predator pressure as well. Three wild canids (Red Fox, Coyote, and Grey Fox) plus domestic dogs. Bobcats with a penchant for harem masters and domestic cats that will take chics up to one pound. Raccoons, Virginia Opossum, Badger, Mink, Striped Skunk weasel go for all life-stages. Redtailed Hawks and Coopers Hawks, are here year round and the larger and sometimes more ballsy Feruginous Hawk is here during the winter. The Great-horned Owl that can take down adult wild Turkey and visit nightly for six months at a time and when young I can have 3 juveniles hunting my pasture all at same time plus parents coming in on occasion. Large Bull Snakes, Black Rat Snakes, and Speckled King Snakes, Copperheads all pose threats to chicks where the Bull Snake can handle birds pushing a 400 grams. Some small rodents (species not known with certainty) will first attack feet of chicks under hen then drag them off to be consumed. I have ants as well and they have forced hens to abandon nest.
My flock is closed nor do we vaccinate. Dogs go after all the predators indicated above with vet bills resulting from a bout of Parvo and a Copperhead bite.
You can make serious inroads with your fowl, especially if they have a little domestic in their background, by taming hens as chicks then having bring chicks to you to be hand fed later. The pure Red Jungle Fowl appear to have behavioral plasticity similar to crows where taming is relatively easy so long as you do not stress them by over-handling or improper movements for being in close proximity to wild animals.
The dispersal part is problematic and not restricted to Red Jungle Fowl. Sometimes my young adult American Games will disperse into woods or fence row far enough their new home range does not overlap with my managed areas. If not retrieved, then outlook for those birds is not good unless predator abundance is low.