Yep, that's pretty much it. This was made a long time ago, before anyone (that I knew of at least) had a great understanding of the editor's deeper functions.

Create a new LosB with an invisible model, and a new XNT with shorter range with an invisible model. Create new cliffs with the 3D tools, then use the pathing tool to be a cliff. Then ring the perimeter of your new cliffs with the invisible LosBs, then inside that make another ring of XNTs. This gives units "on the cliff" vision while those "below" don't. Ramps are made by making them unbuildable and careful placement of the LosB/XNT ring across them.