Well, some of my systems "average down" to a certain extent. By allowing the system to open up new positions on the same symbol, you're allowing for that. I think it's easy to see the result of this in backtesting. The more you allow for multiple positions on the same symbol, typically the better your system does. But this is also a clear demonstration of survivorship bias. If you have an item that hasn't gone to 0, presumably it's gone up and any averaging down would've taken advantage of the snap back.
I usually backtesting with max open / symbol = 1. Then depending on my risk tolerance, I'll open it up to 2 per symbol. This also depends on my overall allocation.
Interesting... What I'd like to know is if anyone has successfully experimented with averaging down. Sorry, don't mean to hijack the thread, but it seems related.