It's $2 per $100k of trade value.
When you trade a 100k USD/JPY lot, you are trading $100,000 worth of JPY. The referenced base currency is the first one.
Now, on my referenced GBP/USD trade, a 100k lot is 100,000 GBP (at exchange rate of, say, $2.01, the trade costs $201,000. Again, the...