I think in reality the two aircraft should have had same ground speed. There will be some minor differences but at 220 kts CAS you should have a TAS of 240 kts and it should take both aircraft 15 minutes to cover 60nm. But reality means 220 kts will not always be delivered. Yesterday I was flying a plane that always flew three or four knots faster than was bugged. Just out of interest, is close enough good enough?