Blood witch + mana tempest interaction

As a blood witch with the sanguimancy ascendency passive, when i cast mana tempest, my life gets drained doing nothing, it keeps draining after leaving the tempest while its effect last.

I have noticed this as well. The cost multiplier is in effect even after you leave the storm, meaning the +2 second baseline duration (+4 with Quality) is actually a nerf to mana and usability.

I want so much to use this spell. It's awesome. But it's crippled by the horrendous restrictions on the spell.