Nobody knows if the place where MH370 gone in water was at fuel exhaustion.
If they supposed the flight was slower (for any reason), they have to make its trajectory more east:
1- To have the frequency drift (from Doppler effect) to remain the same*: it is because the drift is related to the speed of the a/c
relatively to the Inmarsat sat. At 0:11 (UTC) the sat is wobbling to the south, so its speed has to be substract in whole from the a/c speed if the a/c is also going south. If the a/c goes more east with a lower speed, the result of the substraction remain the same, because the sat speed you have to substract is smaller.
2- The time between the path comes into two successive "arcs" (from pings, not published) have to be smaller, so the path have to be "more perpendicular" (to the "arcs").
*More west (mirror path relative to North-South) would have the same effect for the drift, but the "40° arc" at 0:11 could not been achieved).