I have some interesting results. You can force the game to use promeshes all the time. Here are the changes you need to make to the exe to do that:
Address 33592 (hex):
Replace 0F 83 18 01 00 00
With 90 90 90 90 90 90
Address 335A6 (hex):
Replace 0F 84 04 01 00 00
With 90 90 90 90 90 90
If you can't find the correct data at the address, do a search for the data to replace (it should be unique). That said, if it's not at the right address, the code will probably be different too.
So that stops all the awkward popping in and out that can be seen when moving around.
For some reason, the game doesn't seem able to stitch these meshes together properly, especially on edge walls. So you often see into the void. That might depend on hardware/graphics wrapper.
This effect changes with distance. As you get closer to the edge wall, the two meshes get closer and look better (there's no longer a hole).
Trivia:
The two changes to the exe I just mentioned skip two checks. These checks are BEFORE the global "Wall Detail" check. Why? Who knows...
There is a global variable hard coded to be 1.0 that controls how distorted the wall meshes are. Increase it to 100 and they go wild. Decrease it to 0.5 and you can only see a few tiles in front of you. Weird stuff.