Layer became strange when use Blender Plane in Unity2d

First, sorry my bad English.

I make a 2d like model with plural layer structure of Plane in Blender. In the Blender side, I assuming layer artificially by changing the Z-axis.

I used this model for Unity2D with exchange fbx file. and, The expression was well.

But, When read this fbx file to Scene , The layer structure that I set in the Blender side, breaked up It is breaked up , It is not reversed

and more, By the movement of the Main Camera, the strange layer structure changes dynamically too

Please tell me the method that the layer of the fbx file Plane is displayed properly order