diff --git a/debye_bec/bec_widgets/widgets/digital_twin/calculations/calc_varia.py b/debye_bec/bec_widgets/widgets/digital_twin/calculations/calc_varia.py
index 56c235e..db7c471 100644
--- a/debye_bec/bec_widgets/widgets/digital_twin/calculations/calc_varia.py
+++ b/debye_bec/bec_widgets/widgets/digital_twin/calculations/calc_varia.py
@@ -256,6 +256,7 @@ def fm_ideal_pitch(
     Returns:
         tuple[float, float | None]: Pitch of mirror in rad, qy in mm
     """
+    p_cm = bl.cm.center[1]  # posCM
     p = bl.fm.center[1]  # posFM
     q = smpl - bl.fm.center[1]  # dist posFM to posEX
     if fm_focus == "Defocused":
@@ -277,8 +278,9 @@ def fm_ideal_pitch(
         x = 0.098821 * x**2 + 0.512344 * x  # polynom to correct for spot size
         # logger.info(f"x (corrected): {x}")
         y = fm_focy
+        y = 3.183562 * y**2 + 1.258364 * y  # polynom to correct for spot size
         qx = q + x * p / a
-        qy = q + y * q / b
+        qy = q + y * p_cm / b
         f = (p * qx) / (p + qx)  # focal length
         # logger.info(f"qx: {qx}")
         # logger.info(f"f: {f}")