Direction vector that Skybox is visible from

[shinji144]

I've been fiddling with render "holos", and discovered that I could use util.IsSkyboxVisibleFromPoint to draw a line to where your player can see outside a building from, be it a doorway or window. However I've found that certain results don't seem to make sense.
The following examples are near the color room on gm_construct, using the code

local function visibletostring(visible)
    if(visible) then return "Yes"
    else return "No" end
end    
function CanSeeSkybox()
    local isVisible = util.IsSkyboxVisibleFromPoint(LocalPlayer():EyePos())
    Msg("Can See skybox from EyePos? ")
    MsgN(visibletostring(isVisible))
end
hook.Add("RenderScreenspaceEffects", "canseeskybox", CanSeeSkybox)

The first example seems correct, you cannot see the skybox from this position.
[IMG]http://cloud-4.steampowered.com/ugc/708489437356081691/A770A62E4E23EFCC035643C78EA505299B7A30A9/1024x578.resizedimage[/IMG]

However step to the right just a slight bit, and you somehow can see the skybox.
[IMG]http://cloud-4.steampowered.com/ugc/708489437356079211/12BF41B3BBA616CFFF6F1BB028380D2D10C675C9/1024x578.resizedimage[/IMG]

If I step forward a slight bit the skybox also becomes visible from this spot in the color room.

[IMG]http://cloud-4.steampowered.com/ugc/703985853883122089/CF9E63BF220E7B8FA6FC49020E944925A3478E59/1024x578.resizedimage[/IMG]

Can anybody explain how util.IsSkyboxVisibleFromPoint works, or is the function possibly broken/incomplete?
And finally how could I get a direction vector from where we can see the skybox from? (possibly a future feature request)

[shinji144]

Been half a week, was hoping for a reply by now. Any insight to this question would be greatly appreciated.

[OzymandiasJ]

I believe that function returns if the skybox is in your PVS not your line of sight.