I had assumed that I was just eyeballing it wrong. I also just went back to where I had got my info from and it seems I was mis-reading the info there. I was sure that it capped at 5% so I guess I just made what I was reading fit into that lol.
But yeah, you're right. 20% is base. If we can cap it, that's a total of 53% parrying with 5/5 Battuta, 33% without, and here's to hoping that if an AF piece increases Inquartata, it is actually useful to full-time, at least whilst tanking (can we dream of haste, -PDT and inquartata up?)