I tried almost everything I could think of to improve the Pheasant hunting on my lease. I raised and released for a decade. My goal was to multiply the breeders, not so much raise and release to shoot.
The only real success I had was habitat and predator reduction. Fox was our biggest problem, for both Pheasant and Ducks.
One thing you might try is Blackberry thickets, which worked out for me. I also planted some thorny hedges. And let some nearby plots go to weed. A multi-year project.
I tried some Guinea fowl thinking they might have a better chance because they roosted in trees. I found out Guinea fowl are really poor parents, they'd lay randomly all over the place and/or ignore their nest. They slowly vanished over a two year period.
Another thing you might try is watching wild Pheasants. There may be multiple hens in an area and I have no idea why, but they will lay in a communal nest but not sit on it. They eventually lay and sit on their own individual nest and the clutches hatch. I'd raid the communal nest and put the eggs in an incubator, some hatched. Maybe my Hens were just a little nuts or maybe it is a common behavior? I was lucky I had a friend with a couple of large rotary incubators. True wild bird chicks are a lot wilder than semi-domesticated birds, they really need their peace and quiet. If anybody got closer than 30-40 yards or so to my pen their escape instinct would kick in really strong and they'd injure themselves on the pen wire.
The semi-domesticated birds I released would do some really stupid stuff like just stand there in an open field waiting for a Hawk to swoop in, while the wild stock was a lot jumpier and survival savvy, but had a lower survival rate in the pen.