You're right Wilber, as long as your line is going down and back at a 45 degree angle, the weight itself will be at a depth of 2/3 of the amount of line let out. With a Bandit 300, I'd figure one more ft of depth for the crankbait. Look at the "right triangle".
Attachment 166537
As long as your line is going down at 45 degrees, this formula works. As you speed up or have more line out to drag in the water, your angle decreases. Then you would need to use more weight for the formula to work.

