Being, then Mind, then Soul seems to be the traditional reading... Nock's commentary says, "This Mind which perfects our souls is part of the system of Iamblichus, wherein it ranks after Being and before Soul."

For whatever it's worth, it's also crossed my mind as snobbish: of course a philosopher would deify rational Intellect... but why not place Love there, instead? Or Might? (Personally, I was always partial to the Taoist model, which puts Female and Male in the top spot after the ineffable!)

I remind myself that this is just one cosmological model, among many; just like Hesiod makes Eros a primeval, while other authors (Apollonius of Rhodes, Plato, Ovid, Apuleius, etc.) make Him the child of Aphrodite, herself variously sprung from Ouranos or Zeus...