Opinions on a springer power increase

[CapitalBee]

Gents, I have a '73 HW35 (.177, leather piston seal) I've had for about 18 months. Originally doing 10.6fpe, but found to have an Ox spring. I fitted a standard spring and found t was doing 7.5fpe, after fitting a new breech seal. So, I did the breech leak fix advocated by Mick (T20). I also tried to fit a guide and top hat. However, the additional compression left the coil bound, so in a bit of a rush to take the rifle to the last bash, I assembled it without the top hat. Running at 10.3fpe at the bash, a twang was noticeable, so this weekend she came apart again and I took almost two coils from the spring before fitting the top hat and putting her back together. She's now settled in nicely and is doing 11.6fpe. Now the top hat lip was 2.5mm thick max and I removed 6.5mm of spring material, so I wasn't expecting to add to the power (in essence, I've decompressed the spring by 4mm) Or has the decompression, once cocked allowed the spring to release more efficiently? I'd welcome some opinions from people with more tuning experience than I.

NB: the twang has now gone and it's just shot a short string over the chrono' with 4fps variance