An old rule of thumb is the "100 foot" rule for spoons/plugs off of riggers.
60' down, 40' lead off the ball. 90' down, 10' off the ball. I think it was either Yonker or Steinfishki that posted the general rule a couple years back.
This becomes even more important in clear water. Last year at Salmonarama in Racine, we were fishing 40-70fow all week...and didn't take a sniff on spoons off riggers set any closer than 30-50' to the ball. Stretched 'em out and we took fish throughout the day.
I've seen fish hit spoons off 5' leads, but we were fishing 95' down.
If you are running dodgers/flashers and flies off your riggers, you'll want to keep them at 10-15' off the ball to avoid tangles with other lines. Not sure why this works as compared to spoons in shallower water...but it does.
Hope that helps.