I think that's your answer, Fizzygoo, right in your quotes.
To wit, "manifesting does not create a physical form".
And, going back to spell casting, "a magician in the physical world can only cast spells on targets that are in the physical world". No physical form, you're not in the physical world. So a physical mage (non-astrally active) cannot target a manifested mage, by my reading.
Further, "A magician in astral space can only cast spells on targets that have an astral form". Given that a manifesting mage has no physical form, and no mention of becoming dual-natured while manifesting is made, a manifesting mage is still only in astral space. He can now be seen / heard, but only as a ghostly image that can talk with them.