Why a carrier group has no fixed defensive radius

Is a 600-mile defensive circle around a carrier group viable?

Not as a fixed standard; the radius depends on available aircraft and missiles, and 600 miles would require longer-ranged systems.

A carrier group has no fixed 600-mile defensive circle. The radius changes with the aircraft, sensors, and weapons available, and 600 miles was impractical for the force under discussion. Reaching farther would require air defense and missile systems with substantially greater range. The defensible area is a capability outcome rather than a permanent doctrinal number.