AFR misleading? Plugs tell a better story?

Yeah, that valve will soften the hit, and if you have the piston exactly at TDC-compression, hopefully the piston will stay there. You only have a 2 or 3 degree window, before 80psi ( my test pressure) will push the piston down.
You can use less pressure, but it will be less accurate, because, remember your compression results. Furthermore, when the fuelcharge catches fire and expands,the pressure of those gasses in the chamber are gonna sky-rocket. IDK what the ratio is, and it varies continuously with rpm,throttle-opening, and air-density,etc but I imagine it could be many times the compression test numbers. I'll guess the pressure could, at some point, reach 400psi, I mean it's just a guess. So then my test pressure of 80psi is just 5% of that. and the typical tester calls for 30psi, which is less than 2%.
If you just cannot get the crank to hold still, you can back off the rocker gear, and hook the tester up, which will push the piston to the bottom. This doesn't tell you anything about the condition of the top of the bore, or bad lifters, but it will still tell you about the valves and the rings.