Altitude limit on sensor?

I've been trying to work on a security orb of mine. Of course I want to do this at a decent height above my land so I'm not ejecting people I don't intend to while testing. To my surprise it's not working. I was probably at about 400m. Now my demo unit that has the exact same sensor coding is at 145m and works fine. I can not find anything in the wiki to indicate that sensors are restricted to a certain height range above ground level.

Anyone have any thoughts?

There might be one for sensors attached to stand-alone prims; Personally, I can attest to my HUD-mounted sensors working just fine at that height.

I did a little more testing and I think it may be related to my using llOverMyLand. Here is my sensor function:

sensor(integer total_number)
    {
        integer j;
        integer count = total_number;
        for (j = 0; j < count; j++)
        {
            if( isInList(llKey2Name(llDetectedKey(j)), users) == FALSE && llOverMyLand(llDetectedKey(j)) && llDetectedGroup(j) == FALSE)
            {
                llSay(0,"Intruder Detected");
                llSleep(2.0);
                llInstantMessage(llDetectedKey(j), "You are not permitted to be here and will be removed.");
                llSleep(2.0);
                llUnSit(llDetectedKey(j));
                if (removeIntruderMethod == "teleport")
                                llTeleportAgentHome(llDetectedKey(j));
                else if (removeIntruderMethod == "eject") 
                                llEjectFromLand(llDetectedKey(j));
                llSleep(5.0);
                if (alertOwner) 
                      llInstantMessage(owner, "Intruder Ejected" + llDetectedName(j));
            }
        }
    }

Would llOverMyLand return false at a higher altitude? If I eliminate that condition then it works fine. As I said before the one at the lower elevation is using the same condition test before it does anything to the intruder.