Robert Costa's ten nearest neighbors are all journalists — a uniformity that is itself the structural finding. The top 10 scores span a narrow band from 0.99 to 0.99, with David Frum at 0.9951 sitting only fractionally ahead of Philip Rucker at 0.9930, Peter Baker at 0.9923, John Harwood and Katy Tur both at 0.9919, and Ashley Parker at 0.9904. No single neighbor pulls away from the pack; the shape is flat.

The remaining four — Manu Raju (0.9885), Betsy Woodruff Swan (0.9882), Natasha Bertrand (0.9876), and Sam Stein (0.9872) — hold scores within a 0.008-point range of the leader. Every position in the top 10 is occupied by a fellow journalist, with no politicians, government officials, authors, or other subcategories appearing in the set. The audience Costa draws is essentially indistinguishable, in composition, from the audiences drawn by a tight cluster of political and national-security reporters working across print and broadcast outlets.

That kind of same-subcategory uniformity across all ten positions points to a highly specialized audience with little cross-kind diffusion at the top of the similarity distribution.