The Elemental Resistance Adept Power (Digital Grimoire, p. 17) allows the adept to apply "the full rating of the Mystic Armor Power to the character's armor value against [the appropriate] elemental attack type."

There are two ways to interpret this statement, and I hope someone can clarify for me which interpretation is correct. Elemental attacks are resisted with half the value of Impact armor. So, say a character is wearing armor with Impact rating 4 and has Mystic Armor 6, then his Impact armor is 4 + 6 = 10, but halved to 2 + 3 = 5 for elemental attacks. Now, which of the following is correct:

A) If the character has Elemental Resistance for the appropriate elemental attack, then the Mystic armor is treated as being at full value, not half value, and the Impact armor for this attack is 2 + 6 = 8.

B) If the character has Elemental Resistance for the appropriate elemental attack, then the full value of the Mystic armor is added on top of the modified Impact armor, for an Impact armor rating of 5 + 6 = 11.

It grants the full value to your "armor value" (in addition to your regular armor value), so it is subject to all changes the armor value usually is (like being halved by elemental effects). So your armor would then be 4 (regular armor) + 6 (regular mystic armor) + 6 (the power grant you your mystic armor as additional armor value), which is then halved to 8.
Which is effectively the same thing as your interpretation A), although technically you get double your mystic armor and then have to halve it, instead of getting your full value once (which is a matter of semantics only).
Frankly, though, I'd advise using interpretation B) anyways, as the power is weak enough even then.

It is a phys ad power that affects your other phys ad power. It does not effect your physically worn armor, just your phys ad value.

It says you get the full value of your Mystic armor, suggesting that you are using your full value instead of half your value.

So with 4 impact armor and 6 mystic, you would have your halved impact armor of 2, and the full value of your Mystic armor, 6.

Which is a roundabout way of saying I agree with analysis A.