Estimation of Violent Retaliation's extra block chance?

What's the amount of Chance to Block Attack Damage from Violent Retaliation?

The correct, but unhelpful answer is obviously "+1% Chance to Block Attack Damage for each time you've Blocked in the past 10 seconds". That doesn't help much when planning for going to your block cap but not a lot further.

Do you guys with Gladiator builds have a rule of thumb how much block chance from this node one should/can plan with? I'm aware that there is probably not one hard, correct answer (especially as it depends on other mitigation techniques).

I hope this is not a breach of forum etiquette to ask a Duelist related, but non-build question here.