Without running an electronics course I’d suggest you confine modification initially to the following?
Get a good external SWR /power meter and cross check readings with it
Take detailed photos /notes of what you have now (power and winding placements )
Get some plastic sticks and on TX use them to gently compress or stretch the winding and see if things move in the right direction or not?
you don’t need to add/remove turns until you got to fully squashed or fully stretched winding layouts and it was still improving as you did?
Bruce Akhurst