The graphic below is using an equidistant projection, and has a 40° and derived satellite elevation arcs drawn on it from backtracking the data provided by AMSA / NTSB. The red tracks represent the two speeds used by the NTSB and an assumption is made that the aircraft passed well to the west of Aceh, North Sumatra, to avoid PSR detection.
All times shown are UTC, commencing with the LKP at IGARI (1720z) and a possible PSR position at 1822z, all interconnected by an orange track to intercept the possible backtracked position west of Aceh.
The east track has been overlaid with light blue and hourly positions placed on it using a GS of 470 KTS.
Earth-SAT elevation angles are shown for the estimated arcs.
As the projection used is Equidistant, the tracks appear to be diverging to the west. If stretched in a polar direction, i.e. Mercator projection, those tracks should form a straight line and cross all Lat/Long at constant angles. However, if a way-point a large distance away has been entered into the FMS, the aircraft will be following a great circle path and a curved track on a Mercator projection is what one would expect.