high and low power adjusting issue?? (small change)

I have just recently come across a fellow airgunner in my area that owns 22 acres of hunting land I took 3 squirrels at 70 yards on his property.

he was shooting an airforce texan that thing is a beast! And very loud, well we stopped shooting for about 3 mins and in that time 5 turkeys walked with in 40 yards of us and after about 2 mins of trying to get a clean head shot I finally took one it just so happened that there was a twig about ten feet infront of him that my pellet decided to hit first I literally watched my pellet vier to the right missing his head by maybe 1/2 an inch. And then they were gone!

so this buddy of mine gave me a tin of eunjins 43.2 gr 83 count to test for hunting so that I would not have to wait for a head shot next time and tiny twigs wont be as tragic to my ballistics.

so today I spent all day filling my tank and shooting and adjusting my gun, so that I can shoot jsb 24.39’s all day at about 915 fps and then throw in some rat sniper slugs 37 gr hollows, do some quick turns on the hammer and be shooting at about 890- 900.

Heres my dilemma I adjusted my reg to 53.80 OAL. And my valve spring retainer to about 3/4 -1/2 turn after touch, depth is .194. I fill my gun to 230 bar and I was testing going back and fourth to see if the fps would go right back.

Mind you I did this so many times!

First I did 12 shots of jsb at an ave of 915 fps, then I figured out that it took 5 turns from that point to get 828 ave fps with 12 shots using eunjin 43.2 gr, then I turn it back to its exact spot, 5 turns back and did another 12 shots of jsb 24.39s at an ave fps of 884!! That group started at 184 bar. Then I went back to eunjins 5 turns back up, 12 shots at an average 828 again all they way down to 115 bar!?

I did this numerous times with the same result the eunjins fps ave never changed from 230 bar down to 115 bar but the jsbs would drop 25 and at some points 35 fps ave. right around 200 bar and then go back up when it falls off the reg. I even did 2 full sessions of 5 shot groups going back and fourth with the same result.

It does not make sense to me, I figured if I had this problem it was going to be with the heavier eunjins, not the lighter jsbs. And yes I did mark the spots and went back to the exact spot everytime.

has anyone tried to do a high low quick adjust the way I have? And is there a better more consistent way to achieve this goal or is this gun just meant to stay put at one power setting?