Average radii versus orbital period ratios of all 554 pairs of adjacent planets in the radius catalogue. Each point is colour-coded based on the number of planets in the system. There is a weak positive correlation that breaks down when planet pairs with average radii <1 R_⊕ are excluded. Very small and very large planet pairs have predominantly small and moderate PRs, respectively, while the intermediate planets span a much wider range of orbital spacings (Sect. 4).