First of all I doubt it was 13K but regardless the player manned 5 inch guns on the CV's have a long range, are relatively accurate in their aim, and have proximity fuses that ignite the ack when it's close to your plane. The result is you go poof.
Relative to auto-ack, while they don't seem to reach much beyond 7-8K in horizontal distance, they can reach over 20K vertical but actually getting hit by one is rare (although it does happen).