Eye mid plane displacement

Hi everyone,

I’ve been fiddling around with the eye shader provided by epic in the content browser and I am trying to refit it to another eyeball mesh.
I found that the texture map for mid plane displacement isn’t just a linear gradient and is unique to the model, I was wondering if anyone knows how is this map produced, because it obviously has more information than the engine is caring to share.
And it seems to be the vital part for refraction part of the eye.