diff --git a/scripts/Diffraction/single_crystal/base_sx.py b/scripts/Diffraction/single_crystal/base_sx.py
index cc06d2bfd293..d5a46b018ed7 100644
--- a/scripts/Diffraction/single_crystal/base_sx.py
+++ b/scripts/Diffraction/single_crystal/base_sx.py
@@ -284,6 +284,7 @@ def calc_absorption_weighted_path_lengths(self, peak_type, int_type=None, run=No
         default_kwargs = {"ApplyCorrection": self.scale_integrated, "EventsPerPoint": 1500, "MaxScatterPtAttempts": 7500}
         kwargs = {**default_kwargs, **kwargs}
         ws = self.get_ws(run)
+        mantid.SetBeam(ws, Geometry={"Shape": "Slit", "Width": self.beam_width, "Height": self.beam_height})
         peaks = self.get_peaks(run, peak_type, int_type)
         mantid.CopySample(InputWorkspace=ws, OutputWorkspace=peaks, CopyEnvironment=False)
         mantid.AddAbsorptionWeightedPathLengths(InputWorkspace=peaks, **kwargs)
diff --git a/scripts/Diffraction/single_crystal/sxd.py b/scripts/Diffraction/single_crystal/sxd.py
index 5d8d24e5324f..cb4c09885cdd 100644
--- a/scripts/Diffraction/single_crystal/sxd.py
+++ b/scripts/Diffraction/single_crystal/sxd.py
@@ -26,6 +26,8 @@ def __init__(self, vanadium_runno=None, empty_runno=None, detcal_path=None, file
                                <centre x="0.0"  y="0.0" z="0.0" />
                                <radius val="0.003"/>
                                </sphere>"""  # sphere radius 3mm  - used for vanadium and NaCl
+        self.beam_width = 0.6  # cm
+        self.beam_height = 0.6  # cm
 
     def process_data(self, runs: Sequence[str], *args):
         """
diff --git a/scripts/Diffraction/wish/wishSX.py b/scripts/Diffraction/wish/wishSX.py
index ed1c83c6aebd..ef7608c8ab38 100644
--- a/scripts/Diffraction/wish/wishSX.py
+++ b/scripts/Diffraction/wish/wishSX.py
@@ -23,6 +23,8 @@ def __init__(self, *args, **kwargs):
                                <centre x="0.0"  y="0.0" z="0.0" />
                                <radius val="0.0025"/>
                                </sphere>"""  # sphere radius 2.5mm  - used for vanadium and NaCl
+        self.beam_width = 0.2  # cm
+        self.beam_height = 0.4  # cm
 
     def process_data(self, runs: Sequence[str], *args):
         """