We discussed this in another thread not too long ago.
The easiest is probably to just house rule that Mana Barrier Spell is always present on both the Astral Plane and Physical Plane at the same time. Like a regular Ward.
Pros of casting a mana barrier on the physical plane instead of the astral plane:
- It make it harder to cast spells through it (but only) on the physical plane
Pros of casting a mana barrier on the astral plane instead of the physical plane:
- It make it harder to cast spells through it (but only) on the astral plane
- It impose visual modifiers for an astral observer
- It stop wholly astral entities
So, for your analysis, it is mostly correct. Except for:
At the time of casting, a spellcaster must choose whether his Mana Barrier spells is of type Astral or Physical.
It is not different types. The spell is a Mana spell in both cases. Never a Physical spell (such as the manipulation spell Physical Barrier). There are two different locations. Astral Plane or Physical Plane.
What matters is if the responsible magician happen to be on the Astral Plane when casting the spell or if the the responsible magician happen to be on the Physical Plane when casting the spell.
manifested entities (e.g. magicians appearing as "ghosts")
They are still treated as astral entities that only exists on the astral plane (and in the minds of living subjects on the physical plane). A manifested entity have no physical presence and can not interact with anything on the physical plane.
They are only stopped if you cast the mana barrier on the astral plane.
Astral Mana Barrier Also Block -->
2. astral spells (aka "mana" spells)
It make it harder to cast LoS and LoS (A) spells from the astral plane on one side of the mana barrier while targeting a subject or location on the other side of the mana barrier.
In addition to the two things you listed it also impose a visual penalty for astral observers trying to sense things located on the other side of the barrier.
Physical Mana Barriers Also Block -->
1. materialized spirits (I'm assuming there that the spirit loses it's "astral form" when materialized)
They are dual natured entities while materialized and thus present on both planes (and stopped by both mana barrier cast on the astral plane and mana barrier cast on the astral plane).
Physical Mana Barriers Also Block -->
2. all spells (aka "mana" or "physical" spells)
It make it harder to cast LoS and LoS (A) spells from the physical plane on one side of the mana barrier while targeting a subject or location on the physical plane on other side of the barrier.