Non minion skill reservation efficiency while wielding sceptre with Lord of the Wilds

Dear GGG,
as you can expect from the title I specced into Lord of the Wilds today while having 60 spirit available. Used it to power herald of ice and herald of ash.
Equipped 120 spirit sceptre. But heralds suddenly require 60 spirit to run where I was expecting 45 due to 50% less reservation efficiency. So suddenly I can only run one herald. Was this intended or can you share the formula for calculation please? Can provide video documentation if required.

Thank you
kind regards