How do you make additive animation blend correctly?

Hi, I'm trying out animation blending to create variations on my character, something like the character creator in Skyrim. I have a base rigged model in neutral pose, which I saved as a 9 frame animation take of just the same pose. I put that in my base layer in an anim controller. Then I have other 9 frame poses for big nose, big head, etc. and placed them in separate layers so I could blend into them. When I set my blend method to additive, though, the character distorts in crazy ways. Here is some screenshots to show what I mean.

The first pose is the default expression on the base layer, the second is with the bigNose animation set to override the initial animation layer which it does and works fine but the animation now can't be loaded on top of it. Third pose is with the animation layer set to additive. Fourth pose is with the animation set to additive but on my import options I only select the nose joint in the transform mask section.

Am I doing anything wrong with my animations to get this distortion?

Thanks!