Kalibrgun Cricket tuning question

I'm playing with my Cricket Carbine, and am getting some funny results

Kalibrgun reg at factory setting, hammer at factory, which is turned in probably 3 turns or so from flush.
Results 18gr pellets 927 fps avg, 6.1 es

turned down reg 1/12 turn, backed hammer out 2 turns
Resulst 18gr 915 fps 6.1 es

turned reg down another 1/12 turn, hammer out 1 turn (total of 3 out)
Results 848 fps, 9.6 fps es

turned reg way down, like 1/8 turn more turns, hammer out flush with receiver
Results 16gr 900 fps, 9.5 es

installed brand new Huma reg, set at 100 bar, hammer out flush with receiver
Results 16gr 898fps, 4.4 es

I'm turning the reg adjuster clockwise, which should make the reg pressure less as the travel is less??

I can't seem to get the gun to shoot any less than 900 fps no with 16gr or 850 with 18gr pellets. The rifle shoots very accurate, but does seem loud to me with several different moderators. It was tuned really hot when I got it and yet it shot the best 100 yard group I've ever shot, so accuracy is not a problem. It seems no matter where I set the reg, or hammer, it keeps a very tight extreme spread also.

Any thoughts?

My next thought is to turn the reg all the way down to lightly seated on the piston, then start backing it out and little at a time and see where it goes????
 
Your last statement is probably one of the best ways to get there. Sounds like it's ported very efficient. You might also measure the hammerspring. If it was previously tuned hot it might be a heavier wire. Possibly use a lighter spring. Post up the OD, Length, and wire thickness. I'll check to see if I have anything I think would work.
 
Ok, new day, new adventure.

Set Huma @ 135 bar, hammer spring 1/2 turn out from max and results
16gr @ 825 fps, 7 es......go figure?

It seems fromt his that I'm getting into the "range" of the heavy hammer spring, with pressure resistance from the higher reg setting.
If I'm right, the original reg must have been set ~ 125-135 bar. That would all make sense. To get to 900 plus fps, you would need slightly less plenum pressure/reg setting, and the heavy hammer spring would overcome the pressure and give more dwell.