I have a new transducer, R109LHW, 2K. Does anyone have advice about ideal frequencies to choose for low and high for fishing Tuna and looking at a 300' range? I'm looking for bait and Tuna marks. I have tried a variety of combinations and can't quite figure what works best. I almost feel like 50 on low and 200 on high work best but I feel like that kind of defeats the purpose of getting a multi frequency transducer. Those are common to most cheap transducers so I'm sure I'm not dialing in the right detail.