Lookleft, thanks for your insightful answer.
Given that the distance from IGARI to Penang is 222 NM, there is no requirement for MH370 to commence a descent immediately after the turn back.
It hasn’t reached the VNAV Top of Descent point from FL340 / 294CAS, for an ECON desc speed 268CAS in nil wind and without a Penang STAR or approach loaded.