ph_poly worked perfectly for our A6.314 project, now it doesn't, its been broken somehow.
The key might be, that we had the jet model scaled to .12 its original size, so its entire model size was about one terrain poly in size. The thing is it works perfectly in A7, but from the underside of the terrain, not the top, ie, the terrain performs like a roof. I remember when this was a flag at one stage, in med I think, you couldn't set it but you could see it in model properties.