the outer most points of the final arc are based on long range cruise from last radar position.
That creates range at time points outwards from last known radar position. If any range from ping arc falls inside the equivalent range from last known position ring it reduces the range from that time.
Also if any range from ping arc falls completely outside the range from last known position ring then the aircraft was flying faster than long range cruise and this also reduces the further maximum range.
and the same applies for maximum speed calculations and minimum speed calculations.