I visit my one-shot OCs but I live in my longfic OCs

Pretty much all my stories so far have featured a core OC & I realised today that for the couple of one-shots I've done, I have a passing relationship with those OCs, but for the longer stories, it's like I live in the OC's head. Part of it is no doubt the nature of spending months writing from a character's perspective, but it feels odd now that I've recognised it. Like having an alter ego or a twin.

Does this make any sense to any other writers or am I just talking complete nonsense?