Roadster280
There is considerable doubt about the reported height of the aircraft as determined by radar. The INMARSAT data indicates that the aircraft flew at constant altitude and speed in order to reach the area that is now being searched for debris.
Radar tracking of primary returns can be very inaccurate unless a target is being deliberately targetted and tracked. The track and height of MH370 seems to have been derived from sweep recordings of the radar examined after the event. The aircraft was initially flying along civilian airways and not towards any military installations when it turned off its planned flight path. Since the aircraft was assumed to be a civil flight and did not represent a threat, it was not tracked. The estimates of the height and possible altitude changes were all calculated (or estimated) after it was announced that the aircraft had disappeared.
Clearly the military will not want to reveal the capabilities or shortcomings of their radar systems or alert status, so the radar data and height changes reported should be regarded as being possibly inaccurate or not having occured at all.