Looking through the DFRPG magic items book, I see that for armor and shields, the magic bonus for +1 block is 5 times the cost of +1 Defense Bonus, which applies to ALL Defenses...
Am I missing something?
Exploits page 47: Defense Bonus
If you have a ready shield or cloak, add its Defense Bonus (DB) to any Dodge, Parry, or Block roll against an attack that comes from your front or shield side. Defense Bonuses appear on the Shield Table (Adventurers, p. 107).
https://www.screencast.com/t/qJPo0XLuq