Your problem is that you have selected the wrong brief. If you read the FAQ you will see that the brief you have selected gives you the entire FIR plus your departure arrival and alternate aerodromes.
6.1 The briefing will contain information for the whole FIR through which the route passes BUT NOT all the Licensed Airfields as in the Area Briefing.
Airfields included will be the AD of departure and destination and any additional airfields you have entered. If additional AD are required, insert the ICAO Location Indicator in the additional airfields. (DO NOT CONFUSE WITH
NARROW ROUTE BRIEF).
The FAQ are quite well written and I recommend anyone to print them out and refer to them until they are totally familiar with the site.
The one you want is the Narrow Route Brief.
The site now works OK, however work is still needed to make the interface more user-friendly and intuitive, something we are still pursueing.
The use of the terminology "UK ROUTE BRIEFING" confuses many people and we need to find a better alternative.
I have been told that the purpose of the radius field is to define a cylinder of airspace round the departure and arrival aerodromes, within which you will be climbing/descending to/from your cruise altitude. You should get NOTAM from surface to Upper FL+4000 ft within these cylinders. For the remainder of the flight you should get NOTAM from Lower FL-4000ft to Upper FL+4000ft. However the fact that you get the entire FIR anyway appears to negate its usefulness.
Hope this is helpful.
Mike Cross
Representing AOPA on NOTAM issues