I think that the design with the little copper inlets is going to have a major flaw. The pressure of the water is going to come in, and is going to have higher pressure pushing down the first half or so of the inlets, and less pressure on the end. I think it may not be getting enough water to the far side of the inlets. If you had your main inlet right on top, you'd probably have better success. The only problem with it directly on top, is that most of the pressure will be going through the center holes, and not the outside ones.
With your current copper tubes, I think that you could get better results if you used smaller tubes at the beginning, where the main inlet comes in, and bigger ones out on the end. It would force equal pressure across the plate. If you decide to go on the top down approach, you should use smaller diameter inlets in the center, and bigger ones on the outside. That way pressure goes across the entire plate and gives equal pressure to each inlet.
But you don't have to listen to me. Your designs are yielding quite impressive results. Good job!
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