Problem with Businessweek's Backtesting??

Here is the Businessweek backtesting link (free):
http://prosearch.businessweek.com/businessweek/general_free_search.html?mode=advanced

I backtested a strategy that got over 100% return for the top 20 and top 25 results, but when I request the top 15 results, there is only a 20% return!! Anyone else experience this problem?
Any input?

 

I see a stock screener; I don't see a backtester.

 

See results, there will be a graph with 12 months of results.