Aural approach for us was to tune a temperament on the larger piano, then, via by a shared-thirds testing, match the other piano to the first. Then,completely tune the larger one and then, octave by octave, making sure the second stayed acceptable..
By machine, (much more accurate), compare the two "templates", ( accutuner= FAC numbers). If there are any great deviations in the amount of stretch showing, it is easy to meld the two, or alter one to fit the other. It is also easy to test the matching algorithm, tune a few octaves as indicated and listen. The ear is the quickest way to know where you might need to compromise, but having the information to frame the problem is helpful.
The Sanderson machines have a simple button that will compress or expand whatever octave width the particular program you are using is built upon. Makes it very useful for special purpose tuning, (recording studios, concerti performances..).
I was trained as an aural tuner, by the best teacher in at least the U.S., and the machines have vastly improved both my pitch changes and matching two pianos together. It was not uncommon, at the university, to have to tune two D's in separate spaces, and then let them meet that evening for the performance. When ET at 440 was a necessity, getting the piano microphone-ready, (polished unisons), from 10 cents flat in 90 minutes was a straight-forward job, and it worked every time. Hard to beat the memory and consistency of an ETD in those situations.