Someone needs to go back to math class if this is the gold standard. 9 square feet is a patch 3 feet by 3 feet. I think they mean 9 feet square or 9x9 feet, but this is the NY Times.
That would be called a good catch. Nothing like having to stand up for a month, or even three days.
Government docs from 60s stated that 10 sq. ft was sufficient. One picture shown was someone sitting on the floor with knees pulled in to the chest, and under a table that had been reinforced-improvised shelter.
For a planned renovation, there is a 10x10 concrete block area the basement, and ceiling reinforced with a diagonal (cuts the space in half) with the maximum protection in the corner of 50 sq. ft. and that was for 5 people.