A little update on this: https://www.ukhillwalking.com/forums/off_belay/consumer_rights_act_experience_...
Thanks again for everyone's advice in here. I still (stubbornly) couldn't let it go, so sought two independent opinions from registered stove installers in the area. Both were pretty shocked at the flue distance from our gable end, and said it was totally unnecessary – and likely the result of poor planning / bringing the wrong length pipes to the job. They also said it will be less stable.
Cue some lengthy back-and-forth with our installer and a not-so-casual threat citing the Consumer Rights Act (Part 1, Chapter 4, Section 49: Service to be performed with reasonable care and skill), and we're in business. They've agreed to come back and refit the pipe higher, and to within a tolerance of 50-100mm of our wall, all at their cost.
Neighbours are psyched. I'm psyched. Gleefully chalking one up for not going away / being a pain in the arse.
