The avatar concept is different than the manifestation concept, although I may be wrong, since neither apply to me personally. My understanding is that an avatar is a person and simultaneously God. A manifestation of God, OTOH, isn't God. If it was, then you would call Baha'u'llah God, or Muhammad God. The two words, Baha'u'llah, and God would be synonymous, and hence interchangeable. I could be wrong, but I don' think that's how Baha'i' view it. In Hinduism, any version (name) of the supreme God, whether it be Krishna, Siva, Shakti, etc. is interchangeable with the term God. So to me, saying 'Sive permeates the universe, is identical to 'God permeates the universe'.I've just been told that Kriskna was a man who literally advised Arjuna during a war that really happened. Krishna was a manifestation of a diety, a soul released into a bodily form or avatar. The next avatar is Kalki.
Perhaps the distinction is subtle, but its still there.