diff --git a/pm2d/auto_tune.py b/pm2d/auto_tune.py
index 4ca7bc2..3c83b7b 100644
--- a/pm2d/auto_tune.py
+++ b/pm2d/auto_tune.py
@@ -220,8 +220,11 @@ def auto_tune(template_bgr: np.ndarray, mask: np.ndarray | None = None) -> dict:
     else:
         min_score = 0.45
 
-    # angle step: 5° default; se simmetria, mantengo step ma range ridotto
-    angle_step = 5.0
+    # angle step adattivo (Halcon-style): atan(2/max_side) deg, clampato.
+    # Template grande → step fine (rotazione minima visibile su perimetro).
+    # Template piccolo → step grosso (over-sampling = sprecato).
+    max_side = max(h, w)
+    angle_step = float(np.clip(np.degrees(np.arctan2(2.0, max_side)), 1.0, 8.0))
 
     result = {
         "backend": "line",
diff --git a/pm2d/line_matcher.py b/pm2d/line_matcher.py
index a671f3f..b8a41b8 100644
--- a/pm2d/line_matcher.py
+++ b/pm2d/line_matcher.py
@@ -197,12 +197,31 @@ class LineShapeMatcher:
         n = int(np.floor((s1 - s0) / self.scale_step)) + 1
         return [float(s0 + i * self.scale_step) for i in range(n)]
 
+    def _auto_angle_step(self) -> float:
+        """Step angolare derivato da dimensione template (Halcon-style).
+
+        Formula: step ≈ atan(2 / max_side) gradi. Garantisce che la
+        rotazione minima produca uno spostamento di ≥2 px sul perimetro
+        del template (sotto sample il matching coarse perde candidati).
+        Clampato in [0.5°, 10°].
+        """
+        max_side = max(self.template_size) if self.template_size != (0, 0) else 64
+        step = math.degrees(math.atan2(2.0, float(max_side)))
+        return float(np.clip(step, 0.5, 10.0))
+
+    def _effective_angle_step(self) -> float:
+        """Risolve angle_step_deg gestendo modalità auto (<=0)."""
+        if self.angle_step_deg <= 0:
+            return self._auto_angle_step()
+        return self.angle_step_deg
+
     def _angle_list(self) -> list[float]:
         a0, a1 = self.angle_range_deg
-        if self.angle_step_deg <= 0 or a0 >= a1:
+        step = self._effective_angle_step()
+        if step <= 0 or a0 >= a1:
             return [float(a0)]
-        n = int(np.floor((a1 - a0) / self.angle_step_deg))
-        return [float(a0 + i * self.angle_step_deg) for i in range(n)]
+        n = int(np.floor((a1 - a0) / step))
+        return [float(a0 + i * step) for i in range(n)]
 
     # --- Training ------------------------------------------------------
 
@@ -415,7 +434,7 @@ class LineShapeMatcher:
         if original_score is not None and original_score >= 0.99:
             return (angle_deg, original_score, cx, cy)
         if search_radius is None:
-            search_radius = self.angle_step_deg / 2.0
+            search_radius = self._effective_angle_step() / 2.0
 
         h, w = template_gray.shape
         sw = max(16, int(round(w * scale)))
@@ -880,7 +899,7 @@ class LineShapeMatcher:
                 ang_f, score_f, cx_f, cy_f = self._refine_angle(
                     spread0, bit_active_full, self.template_gray, cx_f, cy_f,
                     var.angle_deg, var.scale, mask_full,
-                    search_radius=self.angle_step_deg / 2.0,
+                    search_radius=self._effective_angle_step() / 2.0,
                     original_score=score,
                 )
             if verify_ncc: