How exactly are prefabs tagged with PrefabAssetType enums?

So... I have looked this up, but information seems scarce. The enum values and descriptions here: https://docs.unity3d.com/ScriptReference/PrefabAssetType.html are quite confusing. My goal is basically to determine whether an object is a prefab in the project windows that lives in my assets, or an instance that exists in the scene. I was trying to do this with gameObject.scene.name==null, but that seems to have changed since nested prefabs were introduced and it is very hacky anyway. So in Reset() and OnValidate(), I am calling PrefabUtility.GetPrefabAssetType(this.gameObject) and setting a bool which can be checked at runtime. Or I am trying to. I do not understand the output I am getting from the function at all. It looks like when I have a prefab in my project folder it returns PrefabAssetType.NotAPrefab, but when it checks the prefab instance in the scene, it returns PrefabAssetType.Regular? To me, this seems like very weird behavior? And I don't understand what PrefabAssetType.Variant would be at all... Can someone please clearly explain to me exactly what the types are and how prefabs are tagged? I'm very confused if this is even the intended behavior or if I've somehow broken something as it just seems to be very counter intuitive labeling, or I am missing something about how prefabs are categorized(and it is probably the later)