The difference is caused by the speed restriction that is included in the AFM limitation required by AD 2018-08-03 for airplanes with Package C engines. In addition to the 140 minute limit, the limitation also states, "ETOPS single engine driftdown diversion must be planned and flown at engine-out long range cruise speed." This speed is less than the speed operators normally use for ETOPS route planning, so the ETOPS circle radius per hour of diversion flight is less than it would be if there was no speed restriction. The speed restriction results in engine operating conditions that reduce the chance of sitting on a blade resonance. The later AD for package B engines did not have this speed restriction.