I've never seen a machine that could be loaded to its rated capacity and wash properly, and that includes the biggies at the laundromats. I checked this out by weighing loads on a platform scale and found that actual capacity is usually 50-60% of rated capacity. This is not terribly surprising, nor terribly bad news, it's just an empirical factor that can be dealt with.
What I typically do: For front-loaders, i.e. at the laundromat: best bet is to not load above 75% of actual drum volume, and 60% is better (slightly above the centerline) for getting the best washing action. For top-loaders (the Hotpoint auto and the Danby twin-tub), loosely-loaded to about the waterline level or slightly below: drop the stuff in until it comes up to the right level.
Overload story #1: When I lived with my folks, I got used to a certain amount of laundry being a full load (big top-loader, can't remember the make/model). Went to college, with communal coin-ops in the dorms. Tried to put my normal load in the first time. It hardly moved. That was when I discovered that washer tubs come in different sizes

The ones in the dorms were about half the capacity I was used to. I quickly figured out what the problem was and didn't repeat that performance.
Overload story #2: On a trip to the laundromat last year. This cute hippie-looking couple come in with a big hippie backpack full of laundry. Somehow they manage to cram most or all of it into one of the smaller FLs in the laundromat. Along with lots of detergent, to be sure. This I discovered when I heard the motor groaning, and went over to look. It was compacted in there in such a manner that it would have surprised me if the water ever made it to the center of the load. Hey, at least they saved on dryer time!

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