I also found the code where the structure is added to a merc:

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fReturn = AddStructureToWorld( sGridNo, pSoldier->pathing.bLevel, &( pStructureFileRef->pDBStructureRef[ gOneCDirection[ pSoldier->ubDirection ] ] ), pSoldier->pLevelNode );

that means the structures indices are rotated one step in counterclock direction in jsd file and need to rotated back one step clockwise in code.
upDirection [NORTH] returns pDPStructure[1]. (NW,N,NE,E,SE,S,SW,W).