As I gather from the thread you've just started, Pete.
. Be nice if the piston you seek exists in another Gamo model to give you both your stroke reduction and the spring room you seek. If not, to be fair, I think I'd be quite happy with either of the other routes......your existing set-up with reduced stroke and a little less spring room or even the longer, standard stroke, albeit with, maybe, a "lazier" feel.....I wonder if there'd be a slightly longer and softer spring out there that would help?