I play Zoe, a lot- so I’mma just say…
Why?
The damage is calculated after modifiers, so when Zoe hits you with Q- that’s double the damage it would’ve been if she hit you without using E.
However, for some odd reason- Riot added a 30% magic resist shred onto it.
So now, anyone building MR- if hit by Zoe E- practically might as well not build it in the first place- especially if she has Void Staff.
If this is supposed to be say, be her winning thing- like hitting someone with E should always do big damage… why not make the damage amp be pre-mitigation while the Q itself is post? Then she does more true damage than magic damage and you know that if you get hit by Zoe E, your MR doesn’t matter.

The 30% shred just… fucks with me mentally for some reason.
Don’t get me wrong, makes her amazing as a support for a burst mage like Syndra.