explain to me why on this specific shot, C is not a good option?
With C, it's all up to speed. If you're 8" short or 8" too long, you're looking at a much tougher 8ball.
With A, you can be 8" short or 8" too long and still have a great shot at the side pocket. When you cross the position line, especially closer to the object ball, your target area is small. But when you "come into the ball", you're target is huge and you always have a shot