So just a moment ago, i was 100% baffled, almost made a post then realised im a dunce
This picture shows the shield OH magically giving an extra 10% block. I typically use 45% block on a chest piece and 15% as an epic on the OH (its pretty much my standard for survivability, 69% dodge, 60% block and only two crystals affixes)
Just tested it tho, and yes, shields seem to give 10% block. I know it sounds simple but im sure many people of the community wont know about this, and i like sharing information <3