Ridiculous total volume calculations and shipping rates

We’re shipping two boxes to two different Amazon sites. The dimensions for the boxes are normal: 6x9x10 inches and 6x10x5 inches. The total weight of the boxes is simple: 1 and 2 pounds. Yet we were given NO option to choose SPD as the shipping method so the only mode was LTL/FTL. Additionally, the total volume calculation was ridiculous, which possibly led to a ridiculous shipping rate. Where am I going wrong?