We let the combine guy (same guy for 34  yrs) do the "topping off" also. Cart operators (30+ yrs & 6 yrs) just hold their speed/course. Sometimes load out to the end rows w/combine breaking right-cart breaks left. Sometimes we have the cart stop 50' short of end & combine backs up to him to avoid piling shucks/cobs in one spot. Cart driver can't see inside our cart. A taller tractor (4wd) would allow that. Before carts, we'd sometimes unload into straight truck "on the roll" if field conditions allowed. But-that was a long time ago. Sometimes truck driver (me) selected to high a gear initially & was wishing for a "chip" while box was filling. But-that was about 40 yrs before invention of chip or computer. Truck driver couldn't see combine operator, grain or anything then.

We have camera on rear of cart for backing & for watching traffic from the rear while going down the road. 2nd camera sits high on the side watching into unload auger. Sometimes depending on how/where you park semi or wagon, you can't see into the box. With Avalanche cart you can have corn/beans on the ground pretty fast if you're not careful.

That's the way we do it anyway.