I have found in examining the results of my actual trades that removing the top 10% actually has put me into the breakeven/slightly negative category.Usually the win size will not correspond to a normal distribution. If you're cutting losses short and letting profits run, then you should have some outlier trades in the win size distribution. For the test to be valid you need to eliminate the outlier's. I've found that removing the top 5% winning trades (best 5 out of each 100), has been enough to move the distribution to a more normal bell curve.
What does it mean when all of a systems profits come from 10% of the winning trades? That 10% of winning trades actually represents 5% of all trades. The other 90% of winning trades balance out all trades that result in breakeven or negative results.

