diff --git a/site_ansto/instrument/pelican/config/hmm/hmm_configuration.tcl b/site_ansto/instrument/pelican/config/hmm/hmm_configuration.tcl
index db420279..81321e84 100644
--- a/site_ansto/instrument/pelican/config/hmm/hmm_configuration.tcl
+++ b/site_ansto/instrument/pelican/config/hmm/hmm_configuration.tcl
@@ -192,7 +192,7 @@ proc ::histogram_memory::isc_initialize {} {
     # Radius = 2400mm
     detector_active_height_mm 1015
     detector_active_height_mm lock
-    detector_active_width_mm 5000
+    detector_active_width_mm 5235.9888
     detector_active_width_mm lock
     detector_radius_mm 2400.0
     detector_radius_mm lock