Hi Alpal, I may be wrong but I think you may be overthinking the situation. In a newt if the spider is properly centred and you use a sight tube to centre your secondary mirror in the focuser and adjust your tilt to be able to just see all your primary mirror clips your offset should be automatically set. If you cant see all the primary it may be too close to the secondary and need to be moved down the tube.
I guess I may be over simplifying it but I like the KISS method. I may or may not have been any help here.
Cheers and regards, Richard