I think a 3:1 ratio by weight will get you a 6:1 ratio of soybean plants to corn plants. If you seeded 30 lbs of soybeans and 10 lbs of corn per acre you'd get 90-thousand soybean plants and 16-thousand corn plants. Just to compare, a full acre of soybeans might be seeded at 180-thousand and a full acre of corn at 28-thousand or more. So 3:1 is a lot like 6:1 and turns out to be 50-50. I know, seeds per pound wonder all over the place. Point is, 3:1 sounds agronomicaly (?) logical. I tried this once. Lots of folks are successful. Me, not so much.
I hope I did my math right. You can fiddle with the numbers and, if your broadcasting, add some extra for germination failures.