Tree prefab restrictions?

Unity Engine
1

So, I created this tree in Maya. It’s mesh is combined into one. If I don’t, when the player gets close, the trunk disappears, but the tops and moss stay visible, or it simply doesn’t work at all. This image shows the tree in Unity as a single object.

Now, from a distance (billboarded?), they look okay. These images show the tree in the terrain system as a prefab and utilized in the Place Tree tool:

But, get closer (the trees come out of billboard) and the moss disappears:

I have the tree in an “Ambient-Occlusion” folder. I have the leaves and bark set to the Nature/Soft Occlusion, etc. I also set the moss to Nature/Soft Occlusion leaves, to see if that would help.
Are there restrictions to tree prefabs I am not adhering to? I also have a vine wrapped around the tree, but I’ve removed that for now, so I can tackle one thing at a time. Do I need the tree tops, moss, and vine to have the same single texture map, so there are only 2 textures?
Also, I would like the moss to be transparent, so I don’t think I can have it on the same UV map as the tree foliage, or that too gets transparent.

2

Terrain trees can have two materials and two textures for their mesh, usually the bark and leaves. So your moss planes should be mapped to the leaf texture. The vines are trickier – if you can use the same bark texture on them, then that part of the mesh can be assigned the same material. (The bark usually just wraps around and tiles on trunk areas).