diff --git a/src/iterative_ensemble_smoother/experimental.py b/src/iterative_ensemble_smoother/experimental.py
index 632c23af..a11d914d 100644
--- a/src/iterative_ensemble_smoother/experimental.py
+++ b/src/iterative_ensemble_smoother/experimental.py
@@ -306,8 +306,6 @@ def correlation_threshold(ensemble_size: int) -> float:
             if np.all(~unique_row):
                 continue
 
-            # Get the parameters (X) that have identical significant responses (Y)
-            X_subset = X[indices_of_row, :]
             Y_subset = Y[unique_row, :]
 
             # Compute the masked arrays for these variables
@@ -332,7 +330,7 @@ def correlation_threshold(ensemble_size: int) -> float:
                 Y=Y_subset,
                 cov_YY=cov_YY_subset,  # Passing cov(Y, Y) avoids re-computation
             )
-            X_out[indices_of_row, :] = X_subset + cov_XY_subset @ T
+            X_out[indices_of_row, :] += cov_XY_subset @ T
 
         return X_out