Brown trout do not become fixated on taking at levels.
Well, maybe on some waters, or at some times, but not always. I have seen it many times that you need to have your flies coming back at exactly the right level. Two anglers, one on a slow intermediate and one on an intermediate intermediate and one is catching and the other is not, until he changes to the same line. I can cite lots of variations on that, encountered over the years. Back in the late 1980s, the Loch Leven fish were incredibly demanding about fishing depth, and all the regular rods were carrying about 12 different brands of intermediate line with them! I remember one early morning session, fishing 3 in the boat, as we often did back then, and as light broke, the fish started to come on the feed. One rod was on a fast intermediate, one a slow intermediate and one a floater. First, the guy fishing the fast intermediate caught 3 fish, one after the other with no reply from the other two. Then the guy on the slow intermediate caught 3 fish with no reply from the other 2. Finally, the guy on the floater caught 3 fish with no reply from the other 2. We finished with 9 to the boat, and 3 fish each, fishing 3 different lines, but it was very clear what had happened with the fish moving up as the light came.