This is my "take" on your question and it is not THE answer but one of many answers. When I fish wets, I cast them upstream and mend the fly line several times so the wet fly will be sinking as it drifts down stream which would represent a dislodged nymph that is caught up in the current. Once the wet fly reaches the end of the drift and your fly line starts to straighten out, it will cause your wet fly to rise which would represent a nymph coming up from the bottom. Both actions will trigger a strike with a lot of the strikes coming towards the end of the drift as the wet fly is coming up.
Just my thoughts and nothing more....
Fly fishing and fly tying are two things that I do, and when I am doing them, they are the only 2 things I think about. They clear my mind.