Originally Posted by
Kontact
My take on crank length changes is that you are still pedaling around the same center point, so there is no reason to change your saddle height or set back. Any change you make to satisfy one part of the pedal arc is just going to make another part twice as far off.
This is exactly in line with this well-respected UK fitter's advice
https://bikedynamics.co.uk/FitGuidecranks.htm#1
"The usual assumption is that as cranks shorten, the saddle height can go up by a similar amount. This sounds entirely intuitive as saddle height is often defined as the extension of the leg and shorter cranks will result in less extension through the bottom of the stroke. My experience of fitting many people before and after crank length changes is that this is not always the case and depends how you set your saddle height in the first place. An ideal saddle height is in a narrow window or 'sweet spot' between being too high and too low. If you have found this spot, either through trial and error or a good Bike Fitting, the likely scenario is that changing your crank length will result in no requirement to change the saddle height. Essentially the sweet spot is in the same place"
Given your restricted mobility I would try starting off from your original saddle height i.e. equally less leg extension and compression. Also I don't see how crank length has any direct relation to saddle setback.