Need Help With Shot String

Here is my latest shot string with JSB Exact Jumbo 18.13 gr with one rubber o ring behind the tophat starting psi 2550-2600 power wheel set on 0,3. I would like to tighten this string up so I can shoot from a longer distance. Right now I’m only comfortable shooting from 25 yards with this great of an ES. I would like to tighten it up so I can shoot from 50 yards or so. The o ring that I’m using compresses as it is not rigid. I tried using two o rings and turning up the power wheel a little however the velocities were not consistent. For example you would have a shot a five shot string of 984, 955, 975, 965, and then 970 rather than a bell curve. I have the rigid o rings from Talon Tunes but I’m not confident in taking the tophat out without some direction. Also, how do I decrease velocity using the tophat? I have a test box of pellets from Straight Shooters however most of their pellets range from 12 to 16 grains and my gun shoots 15 grain pellets supersonic on the lowest power setting.
1.)error
2.)883
3.)916
4.)916
5.)942 bull
6.)error .5″ high .5″ right
7.)956 bull
8.)957 bull
9.)953 bull
10.)954 .5″ right 2450psi
11.)996 bull
12.)993 .5″ high .5″ right
13.)1001 bull
14.)995 bull
15.)981 .5″ high .5″ right
16.)992 bull 2275-2300 psi
17.)992 bull
18.)980 bull
19.)984 bull
20.)984 1″ high 1″ right
21.)981 bull
22.)984 bull
23.)976 bull
24.)977 bull
25.)969 bull
26.)964 bull 2100 psi
27.)964 bull
28.)964 bull
29.)964 bull
30.)error 1900 psi