I use my downriggers for Coho.
Where I fish I find that going about 70 to 90ft produces Coho but that depth mimimizes the amount of shakers , dinkers and other small fish surface fish.
If fishing tight in near reefs I will go shallower but use planers and a spoon instead of riggers.
At certain times of year, bucktailing and running lures behind the boat in the prop wash can work wonders.
Coho have a reputation for being a shallower fish...but they can be caught on down to 200 ft. or more.
Ironically most of my bigger Coho are taken on normal Chinook gear when I'm running it in the 70 to 120ft zone.
But I'm talking mid ECVI........there are other places around the island where the Coho are much more plentiful and shallower......