I shipped the same bicycle carrier (two different bicycles weighing 3 lbs different) in opposite directions two weeks apart. First shipment was $77.
Coming back it was $177. Fed Ex (after several phone calls and a 2-page letter) blew me off my claiming the second shipment was by a "consolidator" who can set their own rates.
I found the so-called consolidator on the Fed Ex web site and it had a huge Fed Ex banner hanging outside the building. Bottom line is don't trust their shipping table, you can be charged at whatever rate the shipper can get away with.