One thing we do not know which may have affected the range of the aircraft is exactly how far WNW it flew from Butterworth. It appeared to drop off primary radar at 200nm. Further elucidation of this may have been possible by data collected by other agencies not disclosed for security reasons.
However, if this is so, it does make it even more confusing that the final position appears to be closer to Perth. It would help to explain the time and speed, however.