Power setting

I have a Talon SS, 22 cal, 12 inch bbl. I’ve done some extensive velocity testing using mostly JSB pellets of 14.1 gr, 18.1 gr and Barracudas at 21.3 gr. I’ve run the power knob all through the range from 1 to 12. I’ve found that the optimum power setting to be about 7. My testing was using a HPA tank initially pumped to 2900 psi and CO2. Anything above that did not yield any appreciable increase in velocity. Has anyone else experienced the same? BTW, my gun is strictly stock-no mods.