Block Chance + Cybil's Paw

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Cybil's Paw unique states that it gives spell damage per block chance. Without further specifying what kind of block chance is taken for the calculation.

My past experience with all things in the game is that if something is not specified it applies to everything possible.

So my assumption is that my Block Chance in this case is 80%.
53% BC for attacks and 27% BC for spells.
In other words I have 80% chance to block whatever comes at me - 53% of that is applied to attacks and 27% is applied on spells.

So how does this work?
Will getting more block chance being applied on spells increase my spell damage here?

No, it's based on chance to block attacks, and before you ask, it's based on what you see on your char screen, so if you overcapped block chance you will still get spell damage based on 75% block or whatever is your cap.

So, why doesn't it work with spell block?
Two reasons, one wobbly, the other rock-solid.

Wobbly one:
- When the game says 'block chance' in all possible instances it always means chance to block attack, spell block is a special case.

Rock-solid one:
Nothing here is directly affected by same stat twice (indirectly is possible), so, if you had 100% spell block conversion and you increased block chance by 4%, your spell damage would get boosted twice by the same increase, once for block and once for spell block.