The flaw in this analysis is the first flawed step: The two things are not equal to each other. The two flights are not known to be equal to each other in altitude, therefore their comparison to the other thing (the Inmarsat Satellite) is not known to be equivalent.
The Inmarsat satellite orbit at about 22,000 miles. A 10K-20K difference in flight altitude is irrelevant to the characteristics of the radio signals received by the satellite.
An initial search area the size of the State of Alaska would take into account speed differences.
Did not Inmarsat base their conclusions on those other flights(altitude, speed) and not satellite data alone? By Inmarsat’s own calculations they ASSUMED equality of MH370 to the other flights and based their conclusions on those assumptions. Also from one of Inmarsat’s early info releases they stated the PROBABILITY of a southern route was quite high but not 100%. It was Inmarsat’s best educated guess were this flight came down.