Most experienced anglers have their own preference on how far they setback their line from the downrigger canon ball. There’s a lot of variables that can go into deciding what the optimum setback is such type of fish you are targeting, depth and speed, etc. Here’s an easy proven formula that tends to work almost every time in freshwater fishing applications. It is called the “100 Foot Rule”.
Say the starting point is flat lining at 100 feet behind the boat. Once you clip your line into the downrigger release clip, adjust the setback to always add up to 100 feet. So if you are fishing 25 feet deep, the set back is 75 feet, if you are fishing 50 feet deep, the setback is 50 feet, and so on. The deeper you go the tighter you can run your presentation to your canon ball.
Adding a set of lake trolls or flashers such as a Mack’s Lure Flashlite Troll onto your downrigger ball regardless of your set back is always a good idea. The flash and the water displacement created by the flasher will mimic a school of smaller fishing moving through the water. A large 5 to 10 pound canon ball alone could be interpreted as a predator fish which would keep at bay the fish in which you are targeting.