For free sliders, use heavy mono, because it floats more and easier to untangle. Fluorcarbon sinks. Typically, I can see my cheater lure on the graph approx. 3-4' above the main line. I would be apprehensive about using 12lb for a main line with a cheater. A heavier main line bows out more to keep the cheater from getting into the bottom lure. Remember, once the cheater is deployed, you can adjust your downrigger down, but not up or you will have tangles. You can also pin the cheater with a OR-16 red offshore release on the cable and a rubber band to secure the cheater.