BOAC, with respect to your paragraph #3, the better indicator would be to learn the coordinates for the search grid for the pingers. One would expect that the French Navy would first target the most likely area, based on the extrapolated flight path, and the plot of the recovered wreckage and remains as matched against currents and surface winds over time. If repeated sweeps over an area produce nothing, the grid would be expanded.
I have not read if they have deployed side scan sonar to search for wreckage on the sea floor. Knowing the grids for that would also be a clue into where the French Navy thinks major portions of the wreckage are located.
As the pingers are about half way through their battery life, time is becoming of the essence.
In the instance of Air India 182, the recorders were recovered from 2,000 meters and read within about three weeks of the crash. Air India's wreckage was scattered for about five NM along the route of flight axis.