dont think that your doing something wrong on days when the riggers dont fire, some days they might be hot and others completely dead. i think chris' 100 rule is a good place to start. i dont stacked downriggers too often anymore but with that in mind i do like to run mupped rigs and cheaters. heres an example of a setup:
downrigger rod w/ 20# mainline w/ a smaller spoon 15-25' behind ball. i lower the ball 8-15' and connect my cheater. for my cheater line i use a 6-8' leader of 30# big game w/ a roemer liberator release w/ a larger spoon. dont feel that you have to use a larger spoon above a smaller one. ive found that spoons of the same size work great too. basically you want spoons that are either the same pattern or very similar and always the same manufacturer. i typically run this rig at the very top or the bottom of the active strike range. i dont run this rig extremely deep (over 100') or extremely shallow (under 35'). when the rig is really working i might even put the same spoon on another downrigger. heres another example: lets say on my mupped rig i have my bottom spoon down 60' and 20' off the ball w/ a small spoon. 10' above that (which is 50' down for those without a calculator handy) i have my cheater w/ a larger spoon. then ill take a downrigger (on the same side of the boat) and drop it down w/ a small spoon 40-45' down and 35' back.