@bdhsfz6 brings up a good point -- where I buy material, they load with a pretty big Cat loader that has a 10' wide bucket so it doesn't have a lot of room to adjust position over the top of a 12' trailer. I am guessing the bucket can hold 8-10 tons. When I get these smaller loads, the operator almost always picks up a scoop with the corner of the bucket to get a smaller bite. Then he raises it up to measure the load weight and may curl/shake the bucket to drop some out. When he dumps it, it will still have that corner bias and the heap will be bigger on one end. The other day I tried pulling up to the pile from a different direction, thinking that would change things, but the guy still managed to scoop in a way that put more material at the front of the bed.
I might look for two 55 gal drums and strap them into the front of the bed when getting heavy materials. That would at least offset a good amount of volume and weight from the front of the bed. I can take them back out when I pickup a light material like mulch (which I can load to max volume of the box).