V.D283 — Echo Amplitude Model

Echo amplitude bound A_echo/A_main ≤ exp(−γ_τ√λ_{nm}) with T²-corrected γ_τ=π(1+ι_τ²/2) (τ-effective bound). Exact coupling ~exp(−π√λ) conjectural. Mode (1,0): bound 0.036, approx 0.043.