The FAA does like to make things confusing.Welllllll me and @zeusfl got into a little bit of FAA awakening after our long distance flights with spotters.
I was not to happy about it , as to this day I am still a bit confused .
It makes sense to me that, if the pilot can't see the drone, then a spotter should be required in a position where he can see the drone and tell the pilot what to do in case assistance is required to avoid an accident. If you want to fly your drone behind a stand of trees or behind a building, then you need a spotter positioned to watch the drone while it is out of sight of the pilot.
It makes no sense to require that spotter to be "co-located", standing beside the pilot, if then neither of you can see the drone as it passes out of sight behind the trees or building.