@Communicator,
It may be worth the to conduct a full-fledged trial to confirm assumptions about signal strength etc. given the actual type of aircraft, antenna, flight attitude, etc.
The Inmarsat aperture angles have been determined by reference to the node establishment 'pings' tx/rx timings, meaning that the accuracy of the arcs shown is reasonable, though could be subject to some small errors associated with the internal pass-through time of the aircraft SatCom equipment.
EDIT: I made the following comment in
Post #3819 over 12 hours ago;
That timing will produce a position line (in this case a curved one) and the originating signal will be somewhere along that line.