The complete shipping cost is only covered for 2 (exactly 2 pounds, not a fraction of an ounce more) to Zone 4 or less. Sometimes I ship between 2 and 3 pounds to Zone 1 and it costs a little more which I am prepared to pay. I report the full charge, and occasionally the full shipping fee is paid.
There is a limit on how much they will reimburse for a purchased box, whether you purchase it yourself at a different store, or at the location you are at. The limitations are different for every type, and they reinforce these to the penny. There is one box which always costs me $0.09 too much to buy.
Unless you are shipping bell bars or similar hunks of metal, I am hard pressed to figure out what could weigh 17 pounds and still fit into one of the boxes they sell. Maybe multiple 5 pound bags of sugar (anyone notice that 5 poudn bags of sugar now only weigh 4 pounds?), but I am not sure they would fit. Reams of paper from Staples, maybe?
Shopping Southeast Pennsylvania, Delaware above the canal, and South Jersey since 2008