Sky's reasoning is sound. I've used less separation and been OK. Sockeye I had 10 ft depth separation and 10 ft farther back on the bottom line. No line fouls. I have had fouls before and it's no fun, especially running faster on the salt - the tangle is hopeless and will require re-tying everything.

I don't stack unless it's slow fishing as a rule - I find on my 18ft seaswirl three lines is plenty to run - that fourth line can be just too much anyway. The setup I like best is DRon each side and a diver off the back.