Originally Posted by
coasting
When i built my bikes, I didn't know until after it was complete and I rode it a bit. Only then did I know if my fit was alright. On one bike I was comfy with zero set back thomson and on the other a set back ritchey wcs.
strangely I also had to use different width handlebars to get comfy and when I interchanged them, they didn't work. riddle me that one!
I would say you have a lot of company here. Even experienced cyclists that have owned many bikes struggle to replicate a precise fit from one bike to the next. This I believe is because a bike has probably 20 dimensions that matter and they vary a little bit from bike to bike. Change one and the balance is changed. You mention handlebar width...a notable example. Likely the reason is...width of handlbar affects net reach. So your bikes are probably slightly different in reach even though you think they maybe similar and changing say to a wider handlebar makes the effective reach longer.
A number of factors affect reach, including no. of spacers under the stem...sine of the HTA.