Chronus, very interesting map. Did not know it was available as normally OTH radar technology actual operational range is not public domain.
As there is not really much ( if any) traffic flying southbound in this area on that route, it should be relatively easy to look at the tapes to see if an echo existed at the time.
Or the aircraft ( if indeed there was one there ) flew exactly outside of the operational range, reimforcing the idea that this route was not chosen at random .