Walter
First of all remember, we are discussing a scenario. A possible sequence of events.
In the scenario I painted, the one time that JT would have known an almost exact Vis was, on departure at Aldergrove. He was very familiar with the local landmarks.
If he assessed his initial Vis as our (theoretical) 3nms, he would, without further outside influences, expect to see the cliffs at 3nms. When the TANS told him the range was 3nms he would believe it because he "knew" it was right.
I use only the TANS in the scenario, because I have never seen any evidence of any "on land" equipment being invoved.
If it was you will never get anyone to admit it.