Maybe the use of the word "medium" was a bit confusing - sorry for that.
As Jim already explained:
We have split the front up in sectors Flanders North, Flanders South, Marne Region, Verdun Sector and Alsace.
Some zones were "Hotspot" at times, while others were "medium" or "quiet" (Alsace for example is "quiet" all the war time).
The zone activity changed several times for some zones during the war.

The "Air activity" settings in WOFF's "Workshop" are another thing.
The rules in post #1 should make it all clear, or so I hope.
If you still have questions, just ask.

Vice-President of the BOC (Barmy OFFers Club)
Member of the 'Albatros Aviators Club' - "We know how to die with Style!"