They mention in the article that by the end of it's flight, the bullet is flying subsonically and that their bullet is optimized for that subsonic flight so I w

They mention in the article that by the end of it's flight, the bullet is flying subsonically and that their bullet is optimized for that subsonic flight so I wonder if that forms a significant portion of the flight time. If so you could have the sonic boom start to catch back up with the bullet and not get as much delay as at a closer range.