Quote from psytrade:
FX, you crossed the line there. Scale to $100 bill?, let me clear my throat. I find that since no one in the world trades that size, that you might be all alone in your trading. Put in your system a limit on trading no more than 50% of the volume on entry, and see how it trades and how it scales.
This is particularly true in equities. For example I have a system that returns 40% for 30yrs starting at 100k , but when I test it on 10mil, the return falls to 30% because I limit my volume to no more than 50% of the entry bar. This is not entirely accurate, because technically I can also enter on the next bar seeing how long-term the system is, but there is still a noticeable reduction in returns as you scale up.