From a retired letter carrier, that says it all-"if it fits, it ships". I would tell customers to reinforce with the wide carton sealing tape to protect from damage such as puncture and popping open, and be carefull not to cover the computer lables. If the sender overstuffed and damage or loss of contents happens, it is their loss if not insured. If it is overstuffed the clerk may not insure if there is obvious risk. -- I use to tell other carriers when I picked up a heavy flat rate parcel that was packed tight that they got their moneys worth.