I would go with something like E = 8, A body = 5, B head = 3 or 4, C = 3, D = 1, Miss = -10 or -20
Make an E shot lucrative but less than an A body shot if missed slightly.
Good idea. Will need to make up special scoresheets. Complicate your scoring some. Re-write scoring software.
I've always liked the FBI "milk bottle" targets for scoring.