Originally Posted by Conor
It has to be a lens carrier of sone description or a part inside the parallax mechanism
Yep. I suspect it's either the parallax tube along which a coil shaped groove runs which moves the lens as the wheel moves. That or what the lens sits in inside the groove. I think different scopes use different materials and slightly different designs. And added to which the way the coil shaped groove is shaped may increase or decrease the problem.
I'd say there's a fair bit of maths involved in getting the parallax to work how we like it vs lens characteristics. I'd say without chopping one in half there's probably not much to add. I've seen one of my scopes xrayed and chatted to the khales designer and that's as much as I've been able to guess at. Khales guy confirmed my theory of how the parallax worked on a sidewheel scope.
Reckon the ideal way will be to chop up a make of scope known not to shift, of not shift a lot and compare to one that does and perhaps one that shifts like a flick switch.