Your specialized awareness of the strengths and weaknesses of your armor allows you to better utilize it in combat to protect yourself.
Benefit: When wearing armor in which you are proficient, the maximum Dexterity bonus for that armor is treated as 1 greater than normal (for example, a breastplate would have a maximum Dexterity bonus of +4). You know exactly where the strongest parts of your armor (or shield) are, enabling you to twist your body to place those parts between your vital organs and an incoming attack, thus reducing the chance of a successful sneak attack or critical hit.
Your armor or shield may be used as if it had the light fortification magic armor property vs. one attack per round. If it already has the fortification property, the percentage chance of negating a sneak attack or confirmed critical is increased by 25%.
You must be wearing armor or a wielding a shield to use this ability and you must be proficient in that armor or shield. You cannot use this ability if you are denied your Dexterity bonus to AC, are unaware of the source of an attack (because you can’t see the source generally), or if you cannot otherwise react to attacks.