diff --git a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
index e3447b47..16d7300f 100644
--- a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
+++ b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
@@ -194,7 +194,11 @@ _CORPUS = Path(
 # stress worksheet (simulated case 46): closed its last ventilation residual
 # (our Jan ACH 9.14 -> 9.0748 exact; SAP 29 -> 30 = accredited Elmhurst).
 _MIN_WITHIN_HALF_SAP = 0.72
-_MAX_SAP_MAE = 0.80
+# 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,
+# 10-Hour Off Peak). within-0.5 holds 72.5%.
+_MAX_SAP_MAE = 0.79
 _MAX_CO2_MAE_TONNES = 0.09      # t CO2 / yr vs co2_emissions_current
 _MAX_PE_PER_M2_MAE = 3.7        # kWh / m2 / yr vs energy_consumption_current