Broch of Lingro

Having finally found a plan of the Broch of Lingro it is obvious that the line of stones outwith the present drystane wall falls within its compass, you can see where the broch structures respect the cliff edge here. Obviously these ‘lines’ precede the wall but what is their relationship with the broch itself, both spatially and temporally? I think it probably went all the way to the Scapa Distillery outlet as there is at least one more such stone along the path closer to there. Perhaps some of the burnside walls relate to it?