This is one of the fascinating things I learned about all the nuclear testing the USA was doing in the 70s 80s and 90s. They weren’t trying to make bigger bombs (that was 50s and 60s) it was making the same nuclear material in the bomb more completely used. The more of the material use, the less fallout.
For reference, the Hiroshima bomb used less than 2% of its fuel. Of its 64kg of uranium, only about 1kg actually split. The rest of the highly radioactive Uranium was just spread around by the explosion as fallout.