Maybe I have missed something but it seems that calculations of final position based on satnav pings is assuming the signal received at the satellite is strictly Line Of Sight, which may not be the case. There is a well known phenomena called Tropospheric Ducting
E-skip, tropospheric ducting and other VHF propagation phenomena « Engineering Radio
,amongst a few other VHF propagation effects that typically occur in areas of temperature inversions (warmer air above cooler air). Under these conditions VHF signals can travel far beyond LoS range making it nearly impossible to determine the position of the transmitting station.
As a young amateur radio operator I remember holding a conversation with a man in Houston from my apartment in Austin (~200km) using a low power 146 MHz walkie talkie. Since then I have listened to conversations between two people in Louisiana as clear as if they were across the neighborhood as well as an equivalent discussion originating in Oklahoma.
There is a chance, no matter how remote, that the emissions from MH370 could have been caught in a tropo duct for a considerable distance and emerge generally pointed skyward where the satellite picks it up. In that case the ping timing calculated doppler effect may point to a spot the actual aircraft never passed through.