I think the roadmap will be an ongoing item, as more airfields decide to want a unique frequency. For us GA types, (doing General 'Andling,) we would hope not to hear any other transmissions from over 60 miles away. It is probably much worse for the airlines, traveling at FL400, they would not want any other transmissions from over 300miles away.
I listened to the whole of the last flight of Concorde, from Manchester to London. From N Wales I could hear them ask for supersonic above the Severn Estuary, then heard them turn above the Bay of Biscay. I only lost them when they were below 4000 ft on approach to LHR. and of course I cold not hear LHR Tower.
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