Can't get my alpha channel to work for opacity.

I am using the shafts from the Dwemer dungeon set but I want them to appear bottomless. I made a DXT3 texture in PS that is just 100 percent black with an alpha channel. Just a simple circular alpha fade to make it appear as if the shaft gets blacker and blacker as it goes deeper.

I used the retail blackplane01.nif and changed the diffuse texture to my custom texture and left the normal map as default

My texture is in Skyrim\Data\Textures\KingMango\00kmShaftShadow.dds

In NifSkope I made my texture set

textures\KingMango\00kmShaftShadow.dds

But when I drop the mesh in my dungeon, there is no alpha. Is there a flag or setting that I have to adjust somewhere? I noticed the nif has an Alpha float value which is set to 1.000. I was expecting the alpha channel to override this value. I haven't been able to determine any other possible solutions.

Alternatively, if there is a retail asset I could use, that would be dynamite if anyone knows what it's called.