Having said that I can agree that my case is pretty unusual and that everyone should beware of attempting to do something like this. Even for myself I couldn't do it now. (There is a reason I turned my program off.)
How much did you spend before you "tuned" it? How much did you spend afterwards? What were the tax consequences of your trades? Did you make exactly 500k? Have you traded at all since then?
You mentioned that you occasionally "sat in" and took some large losing positions. Were these on purpose? Bugs? Was your exposure actually much higher than you thought? Was limiting contract size enough risk management?
With regard to tuning I may have lost $1000 or so but as I wrote in the article I was able to build a backtesting model that accurately simulated live trading. So once I had that I could basically use it to verify I had sufficient edge to make a profit after covering my commissions.
My risk exposure was very low. When I said large losing positions this meant like $600. But the bottom line is I had a daily stop loss of $3000 enforced at my broker. The most I ever lost was around $2000.
Anyway, there is not really some hidden thing that I am not telling people. It does bug me a bit that your comment is at the top given that it says I'm manipulating statistics and was actually one of the guys that the quants gleefully picked off. I think it's unlikely I traded much with other HFT systems but if I did they certainly lost money.