Iron Fortress and Max Block from POB

I have been playing strength stack for a couple of leagues now, but I have never played the iron fortress version as I love the comfortability of the rare chest giving crit immunity.

This league I have decided that I would like to try out the iron fortress version of this build, but I cannot for the life of me understand how everyone is getting 65% attack block and 71% spell block with this chest.

I understand the keystone versatile combatant is being used.

I understand there is a rune graft to get rid of the downside of iron fortress.

I have 3200 strength for the attack block from iron fortress, (3200/50 is 64% chance to block).

I however cannot get even close to capping block like everyone else on POE ninja.

I have attached Connor's POB here, so you can see his setup. I feel like I am just missing something super obvious that is giving him so much block chance.

https://pobb.in/OVcV-VNw1Pah