The real advantage of GDX is that historically it has a low correlation to IWM. This is why I like trading this instrument. However, in times of high volatility, I drastically reduce position sizing and I NEVER use the leveraged ETFs on GDX.

Anyway, I will revisit some aspects of the GDX model, especially the opportunity to trade GDX when its correlation to IWM is high, which seems to have been the case in the recent weeks.
Thank you for the insight, Pascal. I think the position size reduction under volatile conditions is one of the key observations. At the time of the last two GDX trades the volatility-based stop was 10-12%. Given that at least a partial role of GDX in the EV trading system is to hedge against IWM, a correlation measure against the broader market might be useful.

-Mike