This approach is also known as the "Minto Pyramid." The website "Untools" has a well-written webpage that explains this: https://untools.co/minto-pyramid/
Nice link, thanks! I was put on to this by someone who had done defence work in their past. They used the "Concept of Operations" for their preferred document style which I also like.
Untools itself also inspired some good discussions on this forum (2020, 137 comments): https://news.ycombinator.com/item?id=23339830