Hi Fabio,
FCC does not support more than 3 level of Hierarchy, hence PIA is coming incorrect.
You need to achieve this using Java Mapping or XSLT to organize the hierarchy as an Intermediate step prior to writing it to Receiver FCC.
Refer following for similar discussions & approach:
File Receiver FCC parameters for multiple hierarchies Subnodes in target structure.
File Content Conversion for Multi Hierarchical Structure
FCC For Hierarchical Structure in Receiver Channel - Process Integration - SCN Wiki
Regards,
Azhar