It's a great start, and Sparkie, I did WAG it and couldn't believe the numbers so I ran 'em.

(Holy #(*^, that can't be right!!! Yep, it is!)
You get more bang the buck so to speak for placing them near spawning habitat, but if the fish migrate to deep water during the coldest part of the winter, what do the forage fish have to hide in? Making highways from shallow to deep cover also helps concentrate the fish along those routes, making them easier to target.
The other thing that you are fighting is the decomposition of the trees over time. If you can source other things that don't decompose as fast, that will allow your yearly structure placements to last longer.
Seeing the WR turn around on the smaller fish means that what you are doing is working. After a year or two of doing the same thing, (small openings between the branches) you'll have to start working on placing cover that larger and larger fish will utilize. The larger LMB are not gaining WR because the food for them isn't of the correct size yet, and in sufficient quantity. As the little YOY fish survive year 1, 2 and 3, they will become better food for the larger LMB.