Here is my initial modifications. This seat is .015" across the flat. At this time I don't even know if I can find a machinist to attempt it.
The flow restriction of the stock valve is the port into the barrel. I have a hunch it's like corn in a deer feeder. Because the barrel is much larger than the funnel at the bottom, the corn in the center is dispensed first as it flows out. I believe it is the same in this situation. If the stock transfer port were to be .04908 in lieu of the .02176, you would have seen a bigger drop plugging those bottom holes in the valve. I'm attempting to reduce the area gradually Making the final point of restriction be the base of the bullet. We will have to see what it takes to crack the valve. Unless I misunderstood, Sean determined that a PEEK valve seat is easier to crack open under similar conditions. My plan I guess is you keep adding more COW BELL,, I mean, spring until it peaks then back off a little.