Everything in your post mirrors my own frustration with PCP accuracy. I got so burned out and frustrated in my search for that "pellet on a pellet" accuracy that it chased me out of the sport for several years.
One of the many targets I've created in Photoshop was one with 100 circles with centers exactly .177 in diameter. Every night for months in my indoor shooting range of 50 feet I'd shoot 100 pellets, trying to see how many times I could actually shoot a pellet exactly in the center of each circle. On most days I was lucky if I could perfectly place 25 - 30 or so out of 100.
I practiced all the basics of good shooting: trigger control, grip, breathing, follow through and heartbeat. I bought all the highest end air rifles, Daystate, FX, and RAW and equipped them with decent scopes. I've got enough tins of pellets from every manufacturer that I could probably open my own store.
And none of these efforts seem to make much difference in my search for accurate shooting. I could never figure out why I could string together three or four perfect shots and then all of a sudden there would be one a little left, or a little right, up, down, whatever. And then I'd reach for the scope, a click here or a click there, and everything would be great until it would happen all over again.
So, I've recently reentered the PCP world again but with different expectations. I still shoot the same targets, but no longer expect the perfect score. I've come to accept that there are just too many variables in the PCP world.