diff --git a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
index 5d74b143c..83bec44d7 100644
--- a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
+++ b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
@@ -280,7 +280,18 @@ _CORPUS = Path(
 # (U=0), previously mislabelled a pitched roof so the party override never fired.
 # Combined with main's gable fix: within-0.5 79.5% -> 80.3%, MAE 0.599 -> 0.584,
 # PE 2.71 -> 2.5. Ratcheted.
-_MIN_WITHIN_HALF_SAP = 0.803
+# SAP-10.2 CALCULATOR ACCURACY BATCH (#1656 backlog: #1666/#1667/#1669/#1668,
+# all stacked on the merged 80.3% baseline above):
+#   #1666 normalise dual-encoded main_heating_fraction (decimal vs percent) ->
+#         80.3% -> 80.6%, MAE 0.584 -> 0.578;
+#   #1667 bill metal-framed API windows on the Table 24 metal U-column + FF 0.8 ->
+#         80.6% -> 81.0%, MAE 0.578 -> 0.571;
+#   #1669 convert measurement_type=2 external dims to internal (RdSAP §3.4/Table 2)
+#         -> 81.0% -> 81.2%, MAE 0.571 -> 0.570, PE 2.5 -> 2.4;
+#   #1668 derive wet-underfloor Table 29 subtype (concrete-slab R=0.25) ->
+#         81.2%, MAE 0.570 -> 0.565.
+# Measured within-0.5 = 0.812000, MAE = 0.565082. Ratcheted.
+_MIN_WITHIN_HALF_SAP = 0.812
 # 0.793 -> 0.789 via the §12 Unknown-meter + dual-electric-immersion off-peak
 # trigger (RdSAP 10 PDF p.62): Apartment 241 (main 691 + 903 dual immersion)
 # -5.38 -> -1.05. Worksheet-validated on "simulated case 48" (Elmhurst SAP 57,
@@ -415,7 +426,10 @@ _MIN_WITHIN_HALF_SAP = 0.803
 # ceiling roof-code-3 slice stacking on main's #1662 floor-to-unheated-space
 # fix: merged-corpus MAE measured 0.583761 (within-0.5 80.3%), rounded up to
 # 3 d.p. so the `<=` assert holds.
-_MAX_SAP_MAE = 0.584
+# Ratcheted 0.584 -> 0.566 by the #1666/#1667/#1669/#1668 calculator-accuracy
+# batch (see the _MIN_WITHIN_HALF_SAP note above): merged-corpus MAE measured
+# 0.565082, rounded up to 3 d.p.
+_MAX_SAP_MAE = 0.566
 _MAX_CO2_MAE_TONNES = 0.068     # t CO2 / yr vs co2_emissions_current
 _MAX_PE_PER_M2_MAE = 2.72       # kWh / m2 / yr vs energy_consumption_current