Why doesn't STURDY METAL passive Benefit SORCERY WARD ???

I had a death mail equipped (armour plus evasion) total approx 1600 (when you count the armour plus evasion)

I then equipped a approx 1600 ARMOUR chest piece (warlord cuirass) and I ALSO took the STURDY METAL passive which states that you get 80% increased armour from your equipped BODY ARMOUR which should in turn INCREASE the total amount of SORCERY WARD shield total because of that increase...

Because sorcery ward is supposed to reduce armour and and evasion by 35% after which it takes the total remaining of armour and evasion (after that 35% reduc) and gives you a shield based on 30% of your total armour plus evasion...

since my armour has increased CONSIDERABLY (from 2k to 4.8k with that chest piece) WHY isn't the sorcery ward bigger?

is that a bug? I tried with iron reflexes keystone on and off and I can't get any difference between my two sorcery ward shields...

an approx 9 difference (1741 vs 1749) shield (I use the moderate version of sorcery ward... not the 50% increased one)