I just bought a 2 furrow Ferguson Dearborn plow Type 10 - AO - 28. The 10 means it is ten inches between the plow shares so the furrows are 10 inches wide. what I don't understand is how deep this plow should dig and what are the specific qualities or use of a 10 inch wide furrow. Most are 12 inches or greater in width between the plow shares. Can anyone enlighten me. Thanks!