It doesn't matter if I use the options --import-target-idno (-iti) or --representation-idno (-ri) or both like above. The result is always the same. The media get imported, but as independent objects, not as media representations of the object "Doodle1" with the Object identifier "doodle-2018-1".
Also, I have hit a bug here: the short option -ri does not work, only the long option works.
The option -t "" is there because if it's not, the command exists with the error message "Set 1 does not exist".
Also the --import-mode does not change anything about the result.