Tuning Please help me understand .22 cal. AVA regulator

I'm now on my 3rd copy of this rifle.

Crossman Premiere 14.3gr domed

Filled to 4000psi

Reg @ 1500psi

ZERO turns on Hammer Spring

Starts at 890ish fps pellet on pellet @ 20 yards

Once the fill res drops below 3000psi velocity drops becomes a little erratic (lower then higher +/- 100) but still accurate AND the reg pressure dropped to around 1300psi?! 

Once the fill res drops to 1900 everything goes to hell as if that's what the true regulator reading is

I realize this is like beating a dead horse to many of you - I apologize up front. 

Should I NOT be complaining? I am getting around 70 very good shots as is.

Thanks in advance - Ponz 

EDIT: I just degassed the rifle for a fresh refill and Reg setting. When I bled the main it stopped releasing air at about 1800psi and only let the remaining air out when I opened up the Reg valve some more. WTF?