Jacobi was fascinated by adventure tales with a Southeast Asia setting, particularly in regard to Dutch central Borneo and the Maritime Southeast Asia. Jacobi wrote to officials working in Southeast Asia to obtain details for his stories, and he had considerable knowledge of that background in his fiction. According to Jack Adrian, "He would write to those in charge of far-flung outposts deep in the heart of the Borneo jungle, say, demanding geographical detail, obscure ethnic lore, atmospheric and forestall conditions; anything, in short, you couldn't get out of a book. This way he became an acknowledged expert in a field he had created himself, at the same time inventing whole new fiction subgenres, such as "Borneo terror tale", "New Guinea adventure" and so on. Later he turned the same trick with Baluchistan.