The key to differentiating ENFJs from ENFPs may be in differentiating NJ from NP. The perceptive function is different. ENFJs perceive with Ni, which derives energy from staying with a vision. NJs tend to take in information in the present that will help them reach a certain point in the future, an "objective." On the other hand, NPs are energized by Ne, which follows emergent possibilities. So they take in information that leads to a changing understanding of the world. Notice that this goal isn't time-bound. The process is the destination.
I think ENFPs are truly changelings. Unlike SPs, they're not in the moment in a physical sense, but NPs are really in the moment with their abstractions. Especially with ENxPs, the rapid transformations of the understanding of the world really show up on the outside.
As far as differentiating the way that NFness manifests itself, I'd say the following. Although all NFs are focused on both people and abstractions, xNFJs are more obviously relational and focused on how they stand with people. xNFJs are additionally focused on abstractions that can help them understand and develop relationships. xNFPs are focused on abstractions that will help them understand the world, albeit they understand the world in a very personal way. xNFPs are interested in people as they embody those abstractions.
I'm not sure if I'm making the distinction clear. When I'm having an identity crisis, I'm focused on refining my understanding of the world. This includes understanding people but not in the context of having a relationship with them, more so just about understanding the significance of their lives. I have a hunch that when xNFJs are under stress they focus on getting on the right foot in their relationships and in their projects.
Feel free to share your reactions. I'd like to hear if this resonates with people or not.