Planetary radius vs. orbital period for TOI-789 (“peas in a pod” diagram). Validated planets (b, c, d) are shown as filled symbols and the candidate .04 as an open symbol, with 1σ uncertainties (the candidate’s asymmetric error reflects the radius–impact-parameter degeneracy). The dashed line and gray band mark the mean radius of the validated planets and its ±1σ scatter; the multiplicative period ratios between adjacent planets are annotated. The radii are uniform to within the scatter—d being the mild outlier—and the spacing is regular, both signatures of the intrasystem uniformity discussed in Sections 6.1 and 8.1.