diff --git a/dsp/framed_model.cpp b/dsp/framed_model.cpp
index 0a714f4..eececa3 100644
--- a/dsp/framed_model.cpp
+++ b/dsp/framed_model.cpp
@@ -249,7 +249,9 @@ static void process_band_structural(
         double kfc = static_cast<double>(band.fc) / (sample_rate / 2.0) * (nbin - 1);
         static thread_local std::vector<float> delta_mark;
         delta_mark.assign(nbin, 0.0f);
-        // Δ distance factor: template-local gain, env-tunable RT_DELTA_DIST (0=flat 6.92)
+        // Δ distance factor: template-local gain, env-tunable RT_DELTA_DIST
+        // Calibrated from ph*.npz (dual_b1q_0.5): factor≈3.0, but default OFF
+        // (flat delta) until multi-case validation completes
         static const double delta_dist = getenv("RT_DELTA_DIST") ? atof(getenv("RT_DELTA_DIST")) : 0.0;
         for (size_t k2 = 1; k2 + 1 < nbin; k2++) {
             if (raw_level[k2] <= 0.25) continue;