I would make a couple of suggestions. I have Marauder in .25 caliber, not the .22 you have. I get 42 shots of 40 FPE with 25.39 grain pellets with the regulator set at 1800 PSI. My Marauder is highly modified, which allows me to use a low pressure. In all fairness, I could probably achieve even better results at 1700 PSI.
Air pressure has to overcome losses due to restrictive flow, the greater the restriction, the higher the pressure the regulator has to be set for. The lower the overall efficiency of the air rifle, the higher you must set the pressure to achieve a selected amount of FPE. The loss of efficiency results in a lower shot count, and in some cases, a greater shot to shot FPE variation. I would suggest you upgrade your valve, and increase your barrel transfer port size before you fuss with your pressure setting on your regulator. You can certainly set a pressure (say, about 2000 to 2100) and you would achieve your goals. But these two upgrades would allow you to lower your regulator pressure, because you will have less loss of flow within your air rifle.
