diff --git a/minimateplus/histogram_codec.py b/minimateplus/histogram_codec.py
index beed36f..adc0714 100644
--- a/minimateplus/histogram_codec.py
+++ b/minimateplus/histogram_codec.py
@@ -101,11 +101,13 @@ _BLOCK_SIZE = 32
 # additional validation that we're looking at a real block.
 _BLOCK_MARKER = 10
 
-# Maximum plausible peak-count value.  Normal-range geophone tops out
-# at 10 in/s = 2000 counts at the 0.005 in/s per count scale; even
-# Sensitive range (1.25 in/s FS) wouldn't exceed ~250.  Mic counts run
-# 0..~400 in observed data.  4096 leaves comfortable headroom for any
-# legitimate value across all modes.
+# Maximum plausible peak-count value.  The geophone tops out at 10 in/s
+# at Normal range = 2000 counts at the 0.005 in/s per count scale.
+# Sensitive range (1.25 in/s FS) tops at ~250.  Mic peak counts have
+# been observed up to ~400 (≈ 100 dB(L)) and per the protocol doc can
+# reach ~813 (140 dB(L)).  2200 covers Normal full-scale plus ~10%
+# headroom for quantization edge cases while keeping every physically
+# implausible value out of the PVS computation.
 #
 # Some prod blocks have been observed with peak-count fields whose
 # HIGH byte is non-zero (block[7] != 0 etc.) — observed across BE9558
@@ -116,7 +118,12 @@ _BLOCK_MARKER = 10
 # device writes in some sub-mode (possibly Histogram+Continuous).
 # Until reverse-engineered, blocks exceeding this bound are skipped
 # rather than propagating bogus values into PVS computations.
-_MAX_PEAK_COUNT = 4096
+#
+# Earlier we tried 4096 — that allowed peak counts up to 4096 × 0.005
+# = 20.48 in/s per channel, which produced 35× inflated PVS sums when
+# the extension-byte blocks slipped through.  See feat/wire-histogram-codec
+# branch history for the rollback.
+_MAX_PEAK_COUNT = 2200
 
 # Geo peak scaling: stored as "count × 0.005 in/s" where 1 count = one
 # 0.005 in/s display quantum.  Equivalent to the waveform codec's
diff --git a/scripts/backfill_sidecars.py b/scripts/backfill_sidecars.py
index 2b9533e..bbe0d0f 100644
--- a/scripts/backfill_sidecars.py
+++ b/scripts/backfill_sidecars.py
@@ -287,16 +287,25 @@ def main(argv=None) -> int:
                             or ev.total_samples < derived // 4):
                         ev.total_samples = derived
 
-                # Preserve user-edited review state + extensions from the
-                # existing sidecar (false_trigger flag, notes, etc.) so a
-                # backfill never wipes them out.
-                preserved_review = None
-                preserved_ext    = None
+                # Preserve user-edited review state + extensions + the
+                # bw_report block from the existing sidecar so a backfill
+                # never wipes them out.  The bw_report block originates
+                # from the paired .TXT ASCII report parsed at ORIGINAL
+                # import time (ach forward / direct upload); the .TXT
+                # file is not in the waveform store, so we can't re-derive
+                # it from disk.  event_to_sidecar_dict takes a
+                # BwAsciiReport dataclass (not a dict), so for bw_report
+                # we overlay the existing block after regen instead of
+                # passing it as a kwarg.
+                preserved_review     = None
+                preserved_ext        = None
+                preserved_bw_report  = None
                 if sidecar_path.exists():
                     try:
                         _existing = event_file_io.read_sidecar(sidecar_path)
-                        preserved_review = _existing.get("review")
-                        preserved_ext    = _existing.get("extensions")
+                        preserved_review    = _existing.get("review")
+                        preserved_ext       = _existing.get("extensions")
+                        preserved_bw_report = _existing.get("bw_report")
                     except Exception:
                         pass
 
@@ -311,6 +320,8 @@ def main(argv=None) -> int:
                     review=preserved_review,
                     extensions=preserved_ext,
                 )
+                if preserved_bw_report is not None:
+                    sidecar["bw_report"] = preserved_bw_report
 
                 # Also emit the .h5 clean-waveform file when:
                 #   - it's missing, OR