Material/Astral x Physical/Mana, I thought I understood this but... Options

[Toloran]

Ok, I've read the relevant sections on using spells in the astral and material planes and the difference between Physical and Mana spells several times. Each time, I come up with a slightly understanding of how they all come together >_> So, I need some clarification to make sure I have things correct.

Casting on the Material Plane...
- Physical Spells can affect anything that exists (alive or otherwise) but can't target anything that exists purely on the astral plane (even if it is visible due to manifestation).
- Mana Spells can affect anything that has an astral signature (usually that means anything that is alive but it also includes "undead" with their freakish auras).

Casting on the Astral Plane (here is where I get the most confusion)
- Physical Spells can't be used at all?
- Mana Spells can be used on anything with an Astral Form (not just an astral signature).

Am I getting this correct? The SR4A book explains casting on the Material Plane just fine but kinda glosses over casting on the Astral Plane (as far as I can tell).

[Yerameyahu]

The problem is the rules contradict themselves, but basically people agree on what you've said.