Perfect block and parry mastery interaction with stun length

I did some simple experiments to see the amount that perfect block increased stun length on parry mastery. Check out this video for the results.
https://www.youtube.com/watch?v=d5LDwMgzNiU&t=88s

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Comments
I do wish the Parry Mastery Description would be more exact about how much PB actually affects the time.