Hi Jonathan,
Good question. It sounds like you want to either maximize distance, or minimize deviation from a line of sight, or both. In order to optimize these quantities, you would need to start with a good model that is defined in terms of the quantities that control them (such as L, the length to which it should be stretched, or theta, the launch angle.
Once you have a function that models the resulting velocity and or flight path, you can apply calculus to optimize your results. However, I don't think there is much I could do to help you come up with that model without more intimate experience with the equipment you're using.
