I was in the same general area (maybe 2x2 miles MAX) on Sunday and we caught most of our fish in the size class you mentioned but also caught some shakers too. I think in general, the salmon are pack hunters so if you get one, there are more around. However, I think it would be unusual for a single small fish to be in a big school and less unusual for a bigger fish to be around smaller ones where it can "bully" a meal and not feel threatened.
I've generally read that for big fish, use live bait but i just can't stand, trying to find it in the early AM, caring for it then dragging it at very slow speed. We've caught several board fish over the years on artificials but the only top 3 in our group was in the youth division last year. That said, if you go to KTP, you will notice several spoons marked as "Winni Derby Winner 20XX" so spoons can and do place you in the derby.
Personally, I think it's all luck for the big fish. right place, right time, right speed, right action, right size, right color and fish in the right mood. some years the derby winner was less than 23-24 inches some years it was over 25 so who knows on a given year a 22 inch fish may win you a boat or boatload of cash.
I would never leave fish to find fish at the derby. We are there to have a good time and MAYBE win something but good time is first. If we are on fish and they aren't runts, we'll stay on them. If we dont register a board fish, we still feel that we have "won".
I'd say keep doing what you are doing. Its working you just have to wait for your turn to win.