Is RFY the brand? Ebay shocks, I assume? Nice work on the piston. I think I see that you chamfered the edges of the ports? Good. Sharp edges are how you get cavitation. Did you do the work on a mill? For the peanut gallery, one of the limitations of the ability to adjust damping via the shim stacks is the ability to flow through the piston. Which is why the original piston is so comically bad, and the new piston is an improvement. If you have a rotary table and wanted to commit about 300% more effort, you could do pistons with "wagon wheel" trapezoidal ports to get more open area on the pistons. Also, rebound is a fixed value that only needs adjustment when the oil degrades in velocity (the only force inputs for rebound are the spring and bike weight.) If you iterate, try reducing rebound port area until it becomes a problem. That gives up more piston real estate so you can bias the port area towards the compression side for a wider range of adjustability.