Do you mean how far out are they? I have allways had extremely good luck heading due west until I hit 200' of water then start trolling south. If I'm not hitting fish right away, I troll out a little more. I have fished up to 4 miles out of Newport, but most of the time you don't need to be that far.
Once I find fish I keep circling back until the school scatters or the bite turns off, then move south again.
I think you can catch a silver's just about every where in the ocean during the season, but somethimes the schools stay out a couple of miles.
When in doubt just follow the pukers(charters). Good luck and be safe!