In this work, we report coherent perfect absorption (CPA) of anti-modes in an indirectly coupled magnon–polariton system. By examining both single and indirectly coupled cases, we experimentally distinguish the modal decay rate $\gamma$ from the effective decay rate ${\gamma }_{\mathrm{eff}}$. At CPA, ${\gamma }_{\mathrm{eff}}=0$, leading to a vanishing output and a visually narrow spectrum in the dB scale, while the intrinsic linewidth set by $2\gamma$ remains unchanged, demonstrating that the effective decay rate dictates the spectral amplitude rather than the physical loss. Furthermore, in the indirectly coupled system, CPA persists over a broad, magnetically tunable detuning range, in contrast to the single-detuning CPA observed in the directly coupled case, thereby enabling magnetically reconfigurable and frequency-selective microwave absorbers.

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• Cavity magnonics
• Magnonics
• Magnons
• Optical & microwave phenomena
• Microwave techniques