Since the definition of underwater search areas in the ATSB's report of 26 June 2014, it has always been clear that the "Priority Search Area" of 60,000 square km's, as the name implies, is only a fraction of the area of possible locations of the airplane that are compatible with INMARSAT's data log and the fuel-limited "performance boundary":
(Bolding mine)
This suggested that, for MH370, it was possible that after a long period of flight under autopilot control, fuel exhaustion would occur followed by a loss of control without any control inputs.
Note: (...)
Also allowing for the fact that a maximum glide distance of 100+ NM would result in an impractically large search area, the search team considered that it was reasonable to assume that there were no control inputs following the flame-out of the second engine. Accordingly the aircraft would descend and, as there would be some asymmetry due to uneven engine thrust/drag or external forces e.g. wind, the descent would develop into a spiral.
As the BEA found in their study, in the case of an upset followed by a loss of control, all the impact points occurred within 20 NM from the point at which the emergency began and, in the majority of cases, within 10 NM.