How do Occlusion Portals work in Unity 4.3

Occlusion culling works perfectly otherwise, but I'd need to get doors to cull visibility when they are closed and vice versa. I've tried different static settings to Occlusion Portal and attached different (separate) colliders but nothing helps. Whenever I bake the occlusion it's either full on or full off for Occlusoin Portal without respecting its 'open' variable at all. I trigger the open field from scripts successfully but it has no effect. Unity's Occlusion Culling documentation is so much out of date that it's not even fun. Is there any place I could find more information or is Occlusion Portal so legacy that it isn't supported anymore with Umbra?