Cumulative-Mass Concentration Widths and Delta-Spike Geometry Along the B2 Boundary Band (Non-Holomorphic Fractal Series — Paper 51)

We scan the WBA kernel on the twisted Bird-map Ulam grid at N = 16384 across the narrow band ϵ∈{0.70,0.71,0.72,0.73,0.74} around the B2 anchor cell identified in Paper 48. The cumulative-mass widths satisfy k50 = k75 = k90 = 1 with top1pct = 1.000000 for every ϵ in this band, so the B2 spray observed in Papers 48–50 appears, on these grids, as a literal single-cell delta spike. We then post-process the cached eigenvectors at N ∈{8192,16384} to track the spike location and local profile, finding a numerically stable anchor near x≈0.592 with a mild leftward drift in ϵ and no resolved halo beyond machine noise.