I know how mundane armor works in the system, and it does not help (or substitute for) Defense rolls.
Neither does Magical armor. It does reduce
damage after it is determined if the attack hits.
It works exactly the same way Mundane armor does.
So which of these is true (some contradict each other)? Evocation Armor:
a) costs twice the number of shifts of an equivalent Evocation Block
b) is a Block that cannot be overcome
c) applies for the entire Exchange/Duration in which it is active
d) acts as the Defense roll if it is the highest applicable Defense
e) acts as the Defense roll is all other Defense rolls have failed
f) reduces the stress from an incoming attack after a Defense roll
These three are true
a) costs twice the number of shifts of an equivalent Evocation Block
c) applies for the entire Exchange/Duration in which it is active
f) reduces the stress from an incoming attack after a Defense roll
C also applies to normal evocation blocks, as long as they are not broken.
For me, there is an exception for reactive Enchanted items, where it only lasts for one attack. But that may vary based on rules interpretation.