I've long been suspicious that smaller ports shoot softer, due to cushioning the piston's landing / impact with the end of the chamber (at the end of the second, or in some cases 3rd fwd stroke, allowing for bounce).

http://www.airgunbbs.com/showthread....fter-shot-feel

But simply making a tiny port will mean it has too small a volume, too high a compression ratio, and too much bounce... also crazy small will choke flow too much.

So i'm wondering how soft your 3.4mm ported TX with 20mm long port shoots ?
I routinely reduce my TX ports to 3.5mm now, I much prefer it... but this is at std length ~10mm They will make a bit more power with a 3.7mm port, but not much. Shortening the port to 7.5x3.5 also works well. As in the thread above, LGV 2.6 x 25 is also a very soft shooting gun.

Also probably worth stating for awareness that this will have no real affect on accuracy, as it's all happening way after the pellet has left, but it does make the guns feel nicer, IMHO.