LevelStreamingVolumes with wolrd composition

Hi all,

First off I should say I am relatively new to unreal. I am checking out the level streaming solutions in unreal 4.4

I have got the basics of world composition setup, and the distance based streaming seems to work fine as is.
Here is where I run into a little problem. From what I can tell the world composition only works on a 2d plane, as in, the distance doesn’t work on the Up/down axis.
For the world we are creating, we have a very large open world, but there will also be areas under the ground(such as caves)
I created a new “cave” level and assigned it to a new layer in the world composition window and turned off distance streaming.
As a test I got the cave level to load upon entering a trigger volume. I cant figure out how to attach a level streaming volume to that level, the options are not available in the level details window. Is there any difference in a levelStreamingVolume vs simply making a trigger volume?

The other issue I have run into is, how to unload the levels which are distance streamed upon entering a trigger? Basically, I wouldnt want areas on the surface streaming in if im in a cave system underneath the ground.
Is there a way to do this?

Here is a shabby visual to better explain what im trying to get working

thanks!