Scrap, I agree with jlckmj.....????
If you subtract 6.5 inches from both sides of a 24 foot wall you end up with a wall "about" 23 feet long. Actually exactly 22 feet 11 inches. You seem to be subtracting 6.5 feet from the 24 feet length.
So then when you move in 2 feet on each end from the...