Evasion works as a multiplier against parry, and increases chance to parry.
The size of the multiplier is based on Bushi, Tact, Anat.
Without tact/anat/low bushi the multiplier is small. Therefore, chance to Parry is Parry x (small) evasion factor = small increase on parry chance.
Eg: 40% chance to parry x 20% extra chance = 48% parry chance (chance to evade)
Without parry but high tact/anat/bush Evasion multiplier is large. Therefore, chance to parry is Parry (none) x (large) evasion factor = No change to zero parry chance
Eg: 0% chance to parry x 50% extra chance = 0% parry chance.
However, with JOAT, there will always be a slight chance to parry....
From the FAQ.
Evasion ~ 10 Mana ~ 60 Bushido ~ (Stance) ~ Duration 3s to 7s ~ Recharge 20 s
(Puts you in a evasive stance for a short duration, allowing you to parry magical attacks like dragon's breath and energy bolt.)
What it Does – Evasion dramatically increases your parry chance, also giving you the ability to parry direct damage attacks from other sources, such as spells, and dragons breath. This does not give the evader the chance to parry status effecting spells and abilities, however, if the effect does damage over time, which can be parried, such as poison or bleed ticks.
As of publish 43, Evasion formula underwent some changes and no longer multiplies your block chance by a flat 50%. Instead it is based on your Bushido, Anatomy, and Tactics skills. The duration of Evasion is also influenced by these skills. Examples of the multiplier to the evasion bonus to your parry skill are as follows.
Evasion Bonus : 16% - 40% without GM Anatomy or Tactics
† 42% - 50% depending on level of Anatomy and Tactics skill starting at Grandmaster.
Example – If you have a 30% chance to parry, and your skill combinations net you a 40% parry bonus, your parry chance will increase to (30 * 1.4) = 42% for the duration of Evasion.
