I am willing to bet it's the environment. Home is safe for him. In the field where he hasn't spent much time is still new. He wants to explore but doesn't want to be left behind so he will initially range close but get a few more times out there and let him mature, he will be just in sight range.

I took my dog hunting yesterday. The site next to a busy highway and we were nearing the edge. My dog scented something and ran into the thorny blackberry thicket. Tried to call her back but she wouldn't listen. 20min later a rooster popped up about 30' from where she entered. I can only assume that she was on point all that time because the bushes stilled. Too bad I had my shotgun broke open. Later she ran into the corn fields and flushed/pointed another one. Both times I couldn't steady her because the thicket is nasty. Only small dogs enter in them. In the corn field I can't see her. Oh well.

Have fun hunting with him. If anything else it's valuable experience for the pup.