diff --git a/PopPUNK/__main__.py b/PopPUNK/__main__.py
index c472d74c..436c6c3e 100644
--- a/PopPUNK/__main__.py
+++ b/PopPUNK/__main__.py
@@ -160,10 +160,10 @@ def get_options():
 
     # model refinement
     refinementGroup = parser.add_argument_group('Refine model options')
-    refinementGroup.add_argument('--pos-shift', help='Maximum amount to move the boundary away from origin [default = 0.2]',
-            type=float, default=0.2)
-    refinementGroup.add_argument('--neg-shift', help='Maximum amount to move the boundary towards the origin [default = 0.4]',
-            type=float, default=0.4)
+    refinementGroup.add_argument('--pos-shift', help='Maximum amount to move the boundary away from origin [default = to between-strain mean]',
+            type=float, default = None)
+    refinementGroup.add_argument('--neg-shift', help='Maximum amount to move the boundary towards the origin [default = to within-strain mean]',
+            type=float, default = None)
     refinementGroup.add_argument('--manual-start', help='A file containing information for a start point. '
             'See documentation for help.', default=None)
     refinementGroup.add_argument('--indiv-refine', help='Also run refinement for core and accessory individually', default=False,
diff --git a/PopPUNK/models.py b/PopPUNK/models.py
index 9f98a8eb..b3d97a64 100644
--- a/PopPUNK/models.py
+++ b/PopPUNK/models.py
@@ -586,7 +586,7 @@ def fit(self, X, sample_names, model, max_move, min_move, startFile = None, indi
             raise RuntimeError("Unrecognised model type")
 
         # Main refinement in 2D
-        self.start_point, self.optimal_x, self.optimal_y = refineFit(X/self.scale,
+        self.start_point, self.optimal_x, self.optimal_y, self.min_move, self.max_move = refineFit(X/self.scale,
                 sample_names, self.start_s, self.mean0, self.mean1, self.max_move, self.min_move,
                 slope = 2, no_local = no_local, num_processes = threads)
         self.fitted = True
@@ -597,13 +597,14 @@ def fit(self, X, sample_names, model, max_move, min_move, startFile = None, indi
         if indiv_refine:
             try:
                 sys.stderr.write("Refining core and accessory separately\n")
-
-                start_point, self.core_boundary, core_acc = refineFit(X/self.scale, sample_names, self.start_s,
-                        self.mean0, self.mean1, self.max_move, self.min_move, slope = 0, no_local = no_local,
-                        num_processes = threads)
-                start_point, acc_core, self.accessory_boundary = refineFit(X/self.scale, sample_names, self.start_s,
-                        self.mean0, self.mean1, self.max_move, self.min_move, slope = 1, no_local = no_local,
-                        num_processes = threads)
+                # optimise core distance boundary
+                start_point, self.core_boundary, core_acc, self.min_move, self.max_move = refineFit(X/self.scale,
+                sample_names, self.start_s, self.mean0, self.mean1, self.max_move, self.min_move,
+                slope = 0, no_local = no_local,num_processes = threads)
+                # optimise accessory distance boundary
+                start_point, acc_core, self.accessory_boundary, self.min_move, self.max_move = refineFit(X/self.scale,
+                sample_names, self.start_s,self.mean0, self.mean1, self.max_move, self.min_move, slope = 1,
+                no_local = no_local, num_processes = threads)
                 self.indiv_fitted = True
             except RuntimeError as e:
                 sys.stderr.write("Could not separately refine core and accessory boundaries. "
diff --git a/PopPUNK/refine.py b/PopPUNK/refine.py
index 25054e45..7df0fdc4 100644
--- a/PopPUNK/refine.py
+++ b/PopPUNK/refine.py
@@ -67,6 +67,12 @@ def refineFit(distMat, sample_names, start_s, mean0, mean1,
     sys.stderr.write("Decision boundary starts at (" + "{:.2f}".format(start_point[0])
                       + "," + "{:.2f}".format(start_point[1]) + ")\n")
 
+    # calculate distance between start point and means if none is supplied
+    if min_move is None:
+        min_move = ((mean0[0] - start_point[0])**2 + (mean0[1] - start_point[1])**2)**0.5
+    if max_move is None:
+        max_move = ((mean1[0] - start_point[0])**2 + (mean1[1] - start_point[1])**2)**0.5
+    
     # Boundary is left of line normal to this point and first line
     gradient = (mean1[1] - mean0[1]) / (mean1[0] - mean0[0])
 
@@ -121,7 +127,7 @@ def refineFit(distMat, sample_names, start_s, mean0, mean1,
     if optimal_x < 0 or optimal_y < 0:
         raise RuntimeError("Optimisation failed: produced a boundary outside of allowed range\n")
 
-    return start_point, optimal_x, optimal_y
+    return start_point, optimal_x, optimal_y, min_move, max_move
 
 
 def newNetwork(s, sample_names, distMat, start_point, mean1, gradient, slope=2, cpus = 1):
@@ -299,4 +305,3 @@ def decisionBoundary(intercept, gradient):
     y = intercept[1] + intercept[0] / gradient
     return(x, y)
 
-