I actually believe the "Block chance" and "Guard rate" are two different things. "Guard rate" is from Shield Mastery, and when it triggers, the text "GUARD" appears. "Block chance", however, when it happens, does not show the purple text "GUARD", and it just plays a shield animation and knocks the monster back. When "Block chance" triggers, it also has a chance to activate the Divine Shield. "Guard rate", however, doesn't seem to activate Divine Shield.
I imagine "Block chance" triggers first, AND then if it fails, it's Shield Mastery's turn. So assuming you have:
Lv. 18 Shield Mastery (18% Guard Rate)
Lv. 23 Guardian (23% Block Chance)
Lv. 10 Divine Shield (50% Proc Rate)
It should be like this:
Total hits without Divine Shield: 1,000
Expected "Guardian" activations: 230 (1,000 x 23%)
Expected "Shield Mastery" activations: 120 (770 x 18%)
Expected "Divine Shield" activations, assuming no cooldown: 440 (880 x 50%)
Expected times taking damage: 650 (1,000 - 230 - 120)
Your test shows 228 Guardian activations, so that's about right.
Again, just my guess, I haven't done anything to prove these statistics yet.
I imagine "Block chance" triggers first, AND then if it fails, it's Shield Mastery's turn. So assuming you have:
Lv. 18 Shield Mastery (18% Guard Rate)
Lv. 23 Guardian (23% Block Chance)
Lv. 10 Divine Shield (50% Proc Rate)
It should be like this:
Total hits without Divine Shield: 1,000
Expected "Guardian" activations: 230 (1,000 x 23%)
Expected "Shield Mastery" activations: 120 (770 x 18%)
Expected "Divine Shield" activations, assuming no cooldown: 440 (880 x 50%)
Expected times taking damage: 650 (1,000 - 230 - 120)
Your test shows 228 Guardian activations, so that's about right.
Again, just my guess, I haven't done anything to prove these statistics yet.