Well after it's been sitting in the box for far too long I've today with assistance got the remote anemometer mounted.
The roof apex is 8m high, and then there is a 1m chimney with a 50cm pole and finally the arm of the Davis unit - so pretty near the recommended 10m from ground level.
Picture of the unit in place..
To the north
To the South (right of frame)
To the East
finally the West view.
So hopefully a reasonably good position, and certainly wind readings are much closer to the data from the local RAF airforce weather station than they were from the Vantage Vue alone