PCG on surface of ocean is also under landscape

I’m using the new PCG volume to spawn in some actors. I’d love them to be floating on the ocean. Trouble is I don’t need a bunch of extra actors clogging up my scene by spawning underneath my islands. Here is a shot of the scene. You can see the debug cubes hanging out underneath the landscape.

I’m using a get primitive data set to all actors of type waterbody ocean to put my debug cubes on top of the water. That works, but how do I tell them to not spawn under the landscape layer?