$500 math question on extending ball mount shank

:) Hi, the only math that I know is that my 12" shank was too short for me to fully open my tailgate. The only other shank that I could find that would work for me (same drop) was an 18" shank. I had a new pin hole drilled 2"s back making it a 16" shank and had them cut 1" off of the end to clear my spare tire. I gained 4"s and don't feel any difference while towing.