I am still curious about the second point Dark Sylinc made. I already have the triangles correctly ordered from the farthest to the nearest. What should I do to fix the problem when the triangles are already correctly ordered?
Maybe I am missing something here, but this is just the render queue ID, isn't it? The problem I see when I use scene_blend add or modulative is that the result is never transparent or semitransparent so there is no difference if the render queue ID is higher or lower than the render queue of meshes below, I simply don't see them (because the "fog" mesh is not transparent at all).