ANA that 8 degree pink ring is the horizon line for the POR. That is to say its on the extreme receptive edge of its coverage. Yet it intersects with the strong IOR 40 degree red band which has received all the pings since 01:07am to 08:11am.
So I would say the fact the POR didn't pick up the 08:11am Ping is pure guess and not certain. So far not enough info has been given to us to eliminate that arc in the South China Sea.