If I understand your description correctly, you're getting wear on the feather that's facing down on the arrow shelf. That feather always wears the quickest, and given the amount of shooting you're doing, the wear you describe doesn't seem inordinate. You're figuring your FOC wrong. With those weight heads, you're getting a FOC of about 7-8%. But at this stage of the game, you really shouldn't be concerned with FOC. Your shafts are also probably spined too heavy. They're kicking right, a symptom of overstiffness for a left handed shooter, and given that they don't have a chance to straighten out at 5-6 yards, the nock will be left. An arrow that doesn't penetrate the target straight is disconcerting, but try to not let it bother you. Keep working on your form, and get lighter spined arrows when you can. Good luck.