I think maybe you'd want to posit, rather, a mystical conception of God, one in which God isn't a person. That would make for a contrast with theism, but the contrast would be so strong, I maintain, that it would be consistent with atheism.

Well, not my concept of atheism, but you're the one using the word, so it means what you want it to mean. I'm really just saying that not all of us receive the message you're sending by using the word.