@nick
We don't seem to be using he same ping ring information.
Here's where mine came from.
https://www.dropbox.com/sh/ezs6imv36..._UkCXLEIGDVwQa
It's true that the Malaysians never gave the coordinates for the loss of track. Their tightest definition for that location afik is about 10 miles past MEKAR, your location for 18:22 as stated by them is close enough IMO.
560kts gs is a bit fast for a 777.