PolAgnostic, if my reading of diagram 18 is correct then you are incorrect.
The tip of the arrow and the regular spacing of the ping times are a function of graphic design and not attempting to show the position of the aircraft at each ping.
What is relevant is the interval between displayed ping arcs.
Whilst the greatest interval is the penultimate one, this represents 90 minutes and not the previous 60 minutes. Note also the interval after 1825 is also 90 minutes and not 60.