I am almost certain that astral does not give you extra MR. It is true that the majority of units with astral magic have high MR but if you check their MR the high number is listed as a base, not a number below that with a magic-bonus listed.
Also, a pretender with S10 still only gets 18MR in neutral dominion.
The bless gives MR, but not to the mage iirc(unless he is blessed, of course).
llamabeast said:
Astral gives you more MR up to a limit of 18, after which it has no effect.
I just did a quick test and, unless empowered astral magic doesn't count, this does not seem to be the case.
3 levels of empowered astral magic resulted in a 14MR commander - exactly the same MR as he had with 0 astral magic.
If you God has a natural chill aura then every level of water magic will add one to it's power. Just a function of Breath of Winter and Water magic, but it can help. Same with fire magic and heat/fire shield.