Fluid Topics applies the "Top Map" mechanism.
When you send an archive, all maps that are not nested in another map are detected as top maps, and displayed as publications on the portal.
The following archive results in only Map1 displayed as a publication in the portal:
Map1 ├─ Sub-map-A ├─ Topic-Z └─ Sub-map-B
However, if later an archive is sent with only Sub-map-A, it will not be seen as nested. Instead, it will be detected as a top map, and therefore displayed as a publication.