pg. 132 Compat Spells : "Defense Ratings are as normal, depending on if the defender is on the material plane or astral plane (see p. 161)."
So, even a mage using a Manaball (direct mana spell), the opponent's Defense Rating will be Body + Armor as like against a Fireball (indirekt physical spell)?
"Mana spells interact solely with the astral plane; they may affect living beings, as living beings have an astral component, but they have no effect on nonliving, non-astral entities."
So, if the attacking spell is a mana spell, why we use Armor to calculate Defense Rating ? Maybe a Body + Intuition or Willpower + Intuition would be much proper to calculate it.. or even a Body + Intuition + (5 - Essence) , since it has less affection on non-living materials (and as magic does not like the cybers..)