Before venturing out, I have been trying to plot possible NLOS paths with the optical TX at home (inside) and the RX at a convenient roadside spot at a moderate (local) distance. One possible path is VERY remote down very uneven fenland roads which would have to be navigated in the dark with my wife driving the car. I am thinking about her driving the car. I am not allowed to drive as a result of my stroke. Many of the NLOS paths are blocked by nearby houses and trees. It is a surprisingly hard task.
Back to Google Earth to see where might be worth trying. From previous tests it is necessary to aim very carefully.