Fishing 2 lines from 1 downrigger can take some getting used to. Be sure to keep your set back on the bottom line fairly short to avoid tangling the upper line as you drop the ball down. I prefer to keep the upper line set back to 20 feet or less. As far as vertical spacing I've gone as close as 10 feet whan sockeye fishing to as much as 40 feet. The greater the spacing the more chance the upper line will tangle the lower line when it releases. I have no preference regarding the same side of the boat or not. Be sure to use release clips that have rubber to grip your downrigger cable or the upper release may slide on the cable. I hope this helps.