Gambler

I run them 5 - 25' back.  Running long leads gets them closer to the bottom (cowbells sink and the longer the lead, the more they sink).  If short leads are not working, keep the rigger ball within 5' of the bottom.  Cowbells lose there effectiveness once you are more than 5' off the bottom.  I have messed with this for years and found the number of hits goes way up when the ball is within 5'. 

Cowbells and spin n glows trolled tight to the bottom at speeds less than 1.8 are the way to go to put numbers and bigger fish in the boat.  Dodgers and spin n glows work but not as good IMO.