To me it seems unreasonable or even irrational to assume that a 1400 rounds of fire couldn't get close enough to a balloon moving at less than 1 mph, to damage it beyond flight capability; esp when considering the photo on the front page of the LA Times the next morning. They didn't need a direct hit. Anything in the neighborhood should have been sufficient to take it down. In fact, any of the shells seen exploding in the photo should have taken it down, but it remained aloft for at least another thirty minutes after the photo was taken. Also, no balloon was ever found.
Some eyewitnesses reported seeing a large craft.
Btw, I don't know if I mentioned this earlier in this thread, but my dad was living there at the time and remembered collecting shell fragments the next morning. My aunt was home alone with a new baby and a husband overseas. There was an ack-ack gun in her neighbor's backyard. It was all so terrifying that to this day she refuses to talk about that night.