The worry was that a remote nuclear explosion would not carry the same impact and they only had two bombs at the moment. It would have been easy for the Japanes

The worry was that a remote nuclear explosion would not carry the same impact and they only had two bombs at the moment. It would have been easy for the Japanese militarists to downplay its effect. And it turns out the Japanese military was exactly in such a deep denial. After Hiroshima they said it would take a longtime for the US to build another. After Nagasaki they said so what, we will just retreat to bunkers and force the Allies to invade. After Hirohito decided to surrender, the military attempted a coup.