The JS that is used to choose an existing recording currently appears to only give preference to track length where a multiple recordings have the same title & artist. I think it would be a good idea to give extra weight to recordings that match the search criteria, and are from a release that is already in the same release group that the new release is being added to. Rarely would tracks from different releases (regions, deluxe editions etc.) of the same album differ (except perhaps with 'clean' versions of the album).
As an example, in the attached screenshot, because the existing recording of Guilt from the release 'Welcome Reality' has no track length, it is given as the 'worst' choice match despite being from a different release within the release group being added to. It somehow even manages to appear below a recording from a compilation album which also has no length.