Confused a little

So i got two stamina reduction cost when blocking by 9% so obvs thats 18%, if i put them both on any of my armours does that apply even when i block with my shield or not?

Prolly sounds dumb but when i put both on my shield the 18% didnt show up on my Stats screen but when i did the opposite it did? And if thats the case then putting one of the shield and the one armour is pointless if im not blocking with the shield?