Resonance peak height scales with the strength of the returning echo amplitude

Evidence

Suppose A cos(2π ft) is the fresh amplitude provided by the source, and a cos(2π ft) is the weaker (A > a) returning amplitude, taken to be completely in phase (on resonance, A and a are both positive, say). The average power is proportional to (A+a)2. The enhancement compared to A2 alone is (A + a)2–A2 = 2 Aa+a2, which is smaller as a grows smaller — that is, less tall at the in phase resonance peak if the echo strength a is smaller. — Eric J. Heller, Why You Hear What You Hear- An…, 890