3dsmax multi sub texture not displayed correctly

Hi, I'd like to have multiple texture for eyes to have more expressions for the 3d mesh (a face) BUT what I have for the model in 3dsmax is not displayed as wanted in unity.
In max I have 2 UVWMaps for 2 channels of a multi-sub object textures. The height of the 2 maps are different as you can see in render, but in unity seems that the first in the stack is prevalent.
I upload screenshot and entire project...

What is the best way to have a 3d model with more interchangeable faces, mouth, eyes etc?
Sould I fully unwrap the model and change in the textures only eyes?
I'm still learning, so if my idea is wrong I'll be glad to hear many ideas.

thanks