How about this, provided it's possible, which it ought to be:
Successful Blocks cause <insert effect here>.
I think this is so called rework.
I am not sure Salan and Ghostblade would like a rework or just a re-scale.
For re-scale, I agree on using the entire armour instead of shield.
I would suggest 5-10% as the starting point, and 0.5-1% growth per level. Balance may need more test.
I thought your idea once before. It is cool. We can give a shot on Paladin.