Tracking stops at French coast

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What is the Maximum Range I can Get?

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EDIT
Using aproximate latitude/longitude (51.11, -0.15) given at “My ADSB” page of user richardlawes, I have done a heywhatsthat.com maximum range plot. This plot shows that the natural topology restricts the maximum range to only a thin coastal strip of northern Europe, that also for high-flying planes at 40,000 feet (blue curve). Planes flying at 10,000 feet can be seen up to midway across English Channel (yellow curve).