Actor Merging 'Use Landscape Culling' not working

Merging some cliffs meshes with triangles underground on my scene (everything is on the same Level) with ‘Use Landscape Culling’ (if checked, existing landscape geometry will be used to cull fully occluded triangles) don’t create a culled mesh with less triangles. Is the same result as the normal merged mesh.

I need to set some parameters to the Landscape or what I’m missing?

Thanks in advance!