Reddit reviews Cold War Orientalism: Asia in the Middlebrow Imagination, 1945-1961

Absolutely right - there were campaigns during Korea and Vietnam to do this and it's persisted in today's culture. Some of the ignorant commentors that think these stereotypes come up because people are 'petite' 'or effeminate' are clueless. I can specifically recall a chapter of a book where they discuss this.

edit: I believe it was this one but not 100% sure - there were a few really interesting books on this and there might've been another that I can't remember that was purely focused on American influence in body image.