diff --git a/portfolio/builder.py b/portfolio/builder.py
index 12c42cb..92edd3a 100644
--- a/portfolio/builder.py
+++ b/portfolio/builder.py
@@ -33,24 +33,17 @@ class ThresholdBuilder:
 
 
 class RankEqualWeightBuilder:
-    """Rank all stocks by signal. Buy top N at equal weight. Sell if drops out.
+    """Rank all stocks by signal. Buy top N% at equal weight. Sell if drops out.
 
     Called once per bar with ALL stock signals. Returns per-stock actions.
     """
 
-    def __init__(self, top_n: int = 5, min_signal: Optional[float] = None):
+    def __init__(self, top_n: Optional[int] = None, top_pct: float = 0.2, min_signal: Optional[float] = None):
         self.top_n = top_n
-        self.min_signal = min_signal  # optional floor — skip stocks with signal below this
+        self.top_pct = top_pct
+        self.min_signal = min_signal
 
     def build(self, signals: dict[str, float]) -> dict[str, PositionAction]:
-        """Rank stocks by signal (descending). Top N get 'buy', rest get 'sell' if held.
-
-        Args:
-            signals: {symbol: signal_value} for all stocks on this bar.
-
-        Returns:
-            {symbol: PositionAction}
-        """
         # Filter by min_signal if set
         if self.min_signal is not None:
             signals = {s: v for s, v in signals.items() if v >= self.min_signal}
@@ -58,8 +51,14 @@ class RankEqualWeightBuilder:
         # Sort by signal descending
         ranked = sorted(signals.items(), key=lambda x: x[1], reverse=True)
 
-        top_symbols = set(sym for sym, _ in ranked[:self.top_n])
-        size_pct = 1.0 / self.top_n if self.top_n > 0 else 0.0
+        # Determine top N: explicit count or percentage of available stocks
+        if self.top_n is not None:
+            n = self.top_n
+        else:
+            n = max(1, int(len(signals) * self.top_pct))
+
+        top_symbols = set(sym for sym, _ in ranked[:n])
+        size_pct = 1.0 / n if n > 0 else 0.0
 
         actions = {}
         for sym in signals:
diff --git a/reports/pnl.png b/reports/pnl.png
index df2df5a..c30056a 100644
Binary files a/reports/pnl.png and b/reports/pnl.png differ
diff --git a/reports/summary.txt b/reports/summary.txt
index 22bc0c1..9dab488 100644
--- a/reports/summary.txt
+++ b/reports/summary.txt
@@ -1,13 +1,13 @@
 BACKTEST SUMMARY
 ========================================
-sharpe: -0.2136540474098261
-max_drawdown: 22.08204523900236
-max_drawdown_len: 445
-total_return: -0.011700103856604784
-avg_return: -2.4173768298770213e-05
-total_trades: 586
-won_trades: 287
-lost_trades: 295
+sharpe: 0.12450603119200966
+max_drawdown: 18.40327026827532
+max_drawdown_len: 251
+total_return: 0.04945463098329521
+avg_return: 0.00010217898963490745
+total_trades: 695
+won_trades: 357
+lost_trades: 333
 
 SIGNAL IC
 ========================================
diff --git a/run_example.py b/run_example.py
index faa210a..d5ce262 100644
--- a/run_example.py
+++ b/run_example.py
@@ -83,7 +83,7 @@ def main(forward_horizon: int = 5, universe: str = "csi500", signal_name: str =
         sizer_percent=0.95,
     )
     runner = BacktestRunner(config)
-    builder = RankEqualWeightBuilder(top_n=5)
+    builder = RankEqualWeightBuilder(top_pct=0.2)
     for sym, df in data.items():
         df = df.copy()
         df["signal"] = signal.compute(df).values