Description This paper introduces the convention-corrected coupling κ for dissipative two-channel dynamics and classifies four regimes (null, absorptive, overscreening, anti-compensatory) of the fluctuation absorption rate η. The admissible decomposition family concept, τ-selection taxonomy (channel-independent vs state-coupled systems), and a three-system benchmark panel (Ornstein–Uhlenbeck, Brusselator, Schlögl) are presented. A recurrent absorptive window η ≈ 0.20 is observed in state-coupled systems under moderate noise, with a candidate unifying ansatz via composite dissipation 1 − C(1)^{m_eff}. Four falsifiable predictions are stated. Third paper in the ZFCρ Thermodynamics series. Keywords nonequilibrium statistical mechanics fluctuation absorption rate dissipative systems chemical oscillations Brusselator convention-corrected coupling regime classification cross-scale stability thermodynamic uncertainty Self-as-an-End (SAE) Related Identifiers Is supplement to (ZFCρ Thermodynamics series) 10.5281/zenodo.19310282 (ZFCρ Thermo I) 10.5281/zenodo.19511064 (ZFCρ Thermo II) References (ZFCρ / SAE series) 10.5281/zenodo.18914682 (ZFCρ Paper I) 10.5281/zenodo.19426094 (ZFCρ Paper 54) 10.5281/zenodo.19447349 (ZFCρ Paper 55) 10.5281/zenodo.19476358 (Mass Series I) 10.5281/zenodo.19510868 (Mass Series Convergence) 10.5281/zenodo.19464447 (Four Forces Convergence)