Actually, this system is completely legit. No bugs or anything. ALl you do is setup a custom grid with 1x1, 2x2, 1/2 grid, whatever you need and however accurate you want it by creating and removing (moving and moving back) units to give slight vision, in that time, you simply apply vision to those units which are created, moved, and removed. I would recogmend that you make the grid like 20x20, or bigger. You can then place 1 burrowed unit (stacked = custom) which designates vision types. This would mean, cliff type would detect the cliffs and provent the continued vision in that area.
This is the way we are removing Height Vision Problems in Crescent Dyne RPG.