FedEx Shipping Method for WooCommerce

Add a price adjustment field at the box level for the FedEx Shipping Method extension. I currently ship products in various boxes, some are inexpensive ($0.75) and others more expensive ($3.75). It would be great if I could assign these costs at the box level. Right now I put a price adjustment of $1.50 on both FedEx Ground and FedEx Home Delivery to cover my box costs, but it would be more accurate if it were at the box level versus the service level.