Trying to use the weed eater to knock down grass that is 4 feet tall might work in some situations, but not when the tall grass covers close to an acre.
We're just trying to get it down so we can go ahead and mow without having to go over it 32 times.
Tonight when I was rinsing all the little bits of hay and seeds and leaf and dirt out of my hair, I remembered that people used to use old box springs - the metal ones - to drag/level fields. They pulled them behind a truck or a tractor, usually with some sort of weights (like concrete block)
Something like that would knock down dry grass, wouldn't it?
I don't have an old box spring, but I do have t-posts...and chain...and concrete blocks...and a pickup truck...
...and a strong desire to NOT weedeat anymore out in that field.