Hi!
So basically, an IFCProject contains an IFCSite that has IFCBuilding(s). When you export IFC from Archicad and you go into Solibri, this order or classes appears. When you export from Revit IFC, it starts from IFCBuilding. How can you specify that it's Site, not Building? Obviously the name of the linked model is Site but the name doesn't mean it's gonna be recognized as a class. I hope I was being clear enough! 
Thank you for your attention!