As an update, I've done some calculations, and it turns out that my position sizing is out by a factor of 10 in live trading. I assume that this is related to a conversion error of the "Lot" parameter in the Assets.dta file between Zorro and MT4 via the bridge. As a work around, I will apply a factor of 0.1 to my margin calculation.

I found that this error occurs on my ThinkForex account, but not on my Global Prime account.