@OleOle
The premise of the plane being southbound at 18:39 won't work unless it overflew Indonesian territory, which I consider extremely unlikely.
If we put 9M-MRO's position at 18:29 on the intersection of the ping ring and the FIR boundary (6° 0'5.68"N 96°46'17.43"E) (which is the closest possible position for the plane to have been to clear Indonesian airspace north of the tip) the distance to POVUS (the earliest point of a turn which would clear Indonesian airspace) is about 125nm. That's too great a distance to have been traveled in ten minutes.