Why would you choose the Westerly obstacle as a reference? The FMS/AP can do a letdown to anywhere (as I understand it) - just press the button and it does a target let down pattern to the hover. Doing it 10Nm away from your intended landing site doesn't make much sense.
I'm not suggesting it's the optimal method, but given the length of time they operated with S61s it would make sense as a 'legacy technique'. It would be mirroring the standard method of conducting an offshore ARA to a multi-platform field when your destination is in the centre. With the terrain alerts inhibited and the radar tilted up slightly to reduce the sea clutter, and at 10nm or 25nm to give a good view of the bay, it starts to become a little more plausible.