The theory on the farther the fish get from the salt, the worse biters they become doesn't seem to hold much water. You get guys who are skunked in the estuaries and lower rivers while fish are jumping all around. As evident in this thread, the guys fishing the snohomish - not considered far from the salt by most standards - are having a hard time finding biters.

Anyway, I catch silvers up high on the snoqualmie, green, sky that are very aggressive - even after turning red. Sometimes I think the closer they get to the spawning beds, the more territorial they get - and strike out of aggression. Anyway- all that just to say I think it has more to do with river conditions than it does distance from salt.

Another thing I haven't seen mentioned here is the concept of 'taking water'. Take any pool or run with salmon\steelhead in it, and there will be places that certain techniques will produce better than others. There may even be places where the fish just won't bite - while a little ways away, the fish are very aggressive. Many times it boils down to finding the biting fish - instead of just casting all day to fish that just aren't interested.