It seems to me that it is not possible to create a ToC starting from level 3 (sub chapter). The feature is currently limited to level 1 (Entire document) or level 2 (Chapter) in the Edit Index > Type > Create ToC for… contextual menu of the table of contents.
Anyway I submitted the following request for enhancement:
Does anybody have an idea to circumvent this limitation in the meantime?
I attach an example file of what I mean.