Max-entry-limit-reduced-by-open-position-count-in-a-C-Rotation-strategy

CODE:
using WealthLab.Backtest;
using System;
using WealthLab.Core;
using WealthLab.Data;
using WealthLab.Indicators;
using System.Collections.Generic;
using System.Linq; 

namespace WealthScript1
{
   public class RotationStrategy : UserStrategyBase
   {
      public RotationStrategy()
      {
         AddParameter("N Positions", ParameterType.Int32, 10, 2, 20); 
      }

      //create indicators and other objects here, this is executed prior to the main trading loop
      public override void Initialize(BarHistory bars)
      {
         rsi4 = RSI.Series(bars.Close, 4);
         bars.UserData = rsi4;
         StartIndex = 4;
      }

      //pre-execute, sort candidates by RSI, keep lowest 4
      public override void PreExecute(DateTime dt, List<BarHistory> participants)
      {
         symbolsToTrade.Clear();
         participants.Sort((a, b) =>
         {
            RSI rsiA = (RSI)a.UserData;
            RSI rsiB = (RSI)b.UserData;
            int idxA = GetCurrentIndex(a);
            int idxB = GetCurrentIndex(b);
            return rsiA[idxA].CompareTo(rsiB[idxB]);
         });

         _buys.Clear();

         for (int n = 0; n < Parameters[0].AsInt; n++)
         {
            BarHistory bh = participants[n];
            _buys.Add(bh);             
         }

         foreach (Position p in OpenPositionsAllSymbols)
         {
            //sell positions that are not in the _buys list
            if (!_buys.Contains(p.Bars))
               PlaceTrade(p.Bars, TransactionType.Sell, OrderType.Market);
         }

         string actives = string.Join(", ", _buys.Select(x => x.Symbol));
         WriteToDebugLog(dt.ToShortDateString() + ": " + actives, false);
      }

      //execute the strategy rules here, this is executed once for each bar in the backtest history
      public override void Execute(BarHistory bars, int idx)
      {
         if (!HasOpenPosition(bars, PositionType.Long) && _buys.Contains(bars))
         {
            PlaceTrade(bars, TransactionType.Buy, OrderType.Limit, bars.Close[idx] * 0.98);
         }
      }

      //declare private variables below
      private RSI rsi4;
      private static List<BarHistory> symbolsToTrade = new List<BarHistory>();
      private static List<BarHistory> _buys = new List<BarHistory>();
   }
}