Strong hearted support

Have Strong hearted support gem on my Overwhelming presence aura that says '50% less shock duration on you while a supported skill is active'

Idea was to get boots with 50%+ 'reduced shock duration on you' and be immune to shock.

Tooltip says my shock duration is -78% with boots that have 57% reduced shock duration.

So if you dont have that stat on the boots does Strong hearted even do anything?

Seems it just increases the value of shock duration stat from the boots by 50%.

Anyone understand how this works please?