UOM Weight per Unit Question

I am struggling with setting up some items that I purchase. The are different items which are delivered in bags of various weight (1.25kg, 1.65kg, etc.). The bags are packed into boxes, and each box can hold different number of bags (6, 8, 10 bags). The supplier charges me per kg, yet I want to count my inventory by bags, as we always use a full bag.

I was setting up the items with a default UOM of Kg. In Inventory I used 1.25 for Weight per Unit and Bag as the Weight UOM. I then added 3 UOMs: Kg = 1, Box = 12.5 (10 bags) and Bag = 1.25.

Now when I order this item, and enter 275kg in the amount/UOM it shows the total weight as 343.75kg, while the quantity is 275. It shows the correct Net Weight as 275 if I define the Weight per Unit in Inventory as 1, but that is the wrong value, no?

Where do I go wrong?