Thanks to both of you.
Section 1.3 with its table is interesting.
Although I find 5a and 5b apparently contradicting the norm.
I am trying to get more information from the other course student.
In the meantime, I would appreciate comments from anyone with practical experience of such longer distances for Wi Fi, whether intentional, ie with equipment intended for such ranges; or "unintended".
It can be amazing what happens with radio waves.
Many years back, I was listening to two radio amateurs, one "just down the road" in Edinburgh, the other in New Zealand.
My aerial was the proverbial "short piece of string" to a clothes pole in the back garden, hemmed in all round by buildings.
I don't know the NZ amateur's rig; but the Edinburgh amateur was a Cemetery Superintendent and his various aerials effectively were well clear of any buildings etc, with a public park across the road.
I had no troubles picking up both; but the Edinburgh amateur was having great difficulty receiving the signals from NZ.