How much lightning damage is needed to shock bosses?

Party shock is based on monster base hp, not on hp of the actual monster with party bonuses.
I do 5.03 attacks/second so even a 300 ms shock is good for me as when I attack with cleave, each attack counts as a separate hit and if I would shock, I'd shock twice, which means the attack which follows the shocking attack would deal 80% More damage. However, the shock seems to be extremely rare. I have the static blows and shock nodes as well as level 20 20% conductivity which gives me 20% shock duration and 14% increased chance to shock bumping me to 34% chance to shock. Static blows gives me a 45% increased shock duration and conductivity gives me a 20% increased shock duration for a total of 65%. This means I only have to do 0.385% of the bosses life in damage to shock for 300ms. I'm wondering if bosses have an innate resistance to being shocked, or that their lightning resist/life is so high that even ele weakness + conductivity isn't enough to kill them.