Faces rendering that shouldn't

So, the red box is the leafvis i'm inside. The blue box i highlighted in the sky is an areaportal gap in the skybox "seperation wall" which was implemented for the large blue-grey silo prop on the roof to be visible from both sides of the building.

However, even though the leafvis is surrounded by solid geometry and skybox walls, some roof segments on the other side are still be rendered despite there being a 512+ unit tall skybox brush laying directly in the way.

Quite annoying and so far impossible to rectify.

Before anyone asks if the right hand side of the leafvis can see the far building, no it can not. The top of the dirty-white-wood building has a skybox brush ontop of it. Also, the far buildings are not taller than the 512 unit tall skybox wall this leafvis seems to be able to peer over.

There are 3 horizontal hints, one at the top of the roof that lines up with the top of this visleaf, one ~256 units above that which aligns with the texture seem and another 512 above that at the base of the areaportal.

Originally the skybox couldn't go all the way up because of details at that level on the tower, where the conveyer goes inside the tower. Anyway, i just moved the silo/conveyer to the other side of the tower for the moment and not had it go inside the tower; Which has mostly worked. But i'm trying to complete more of the layout at the end of the track so i can completely cordon the map properly with skybox brushes. Maybe vvis would perform better if it didn't have a massive mess at that end of the map.

*shrug*

It's just a little weird and arbitrary at what is chosen to be rendered through skyboxes. Valve's badwater's tower can be seen fully from both sides of an intersecting skybox brush, but func_detail's are calculated as individual brushes, not as a group if they happen to be in a group, so the 2 supports on the tower, found on each side of the skybox brush, shouldn't render in both areas, but they do.

If you have a func_detail intersect a skybox brush the brush only renders on the side the origin sits. But somehow Valve have managed, in their maps, to get func_details to render both sides of a skybox if and when it intersects a skybox brush.

It's frustrating.

I did a little testing and the prop is rendered based on it's bounding box, or it at least appears to be that way. I threw up a solid skybox brush and it renders both sides, but then vvis starts culling faces on roofs that should render (on the right hand side).

I've just gone for the simplest solution and thrown up a large solid structure there to block the view so even if some textures are rendered at least it doesn't look ugly.