I saw a doc about nuclear weapons that mentioned this one and said that the real reason that no one made them bigger was the fact that they were wasteful. The

I saw a doc about nuclear weapons that mentioned this one and said that the real reason that no one made them bigger was the fact that they were wasteful. The atmosphere is effectively 10 miles high. Once your blast radius approaches that the difference in pressure pushes most of the energy upward above the atmosphere. You don't get the horizontal spread you'd expect as you increase tonnage.