The only reason I can think of for the discrepancy between those FINRA numbers and those I get from stockwatch....is that the stockwatch data is based on shares borrowed and re-sold into the CDN markets, with FINRA representing shares short for RVXCF and sold back onto the OTC market in the US.  

Proportionally though....RVXCF has avg daily volume of 9,982 over the past 3 months as per Yahoo Finance.  RVX by contrast is almost triple that with avg volume of 29,692 (again as per yahoo) and that is just for the main TSX, although I don't think the secondary and dark pool exchanges would bump it that much.

With most of the trading in Canada it makes sense that that is where most of the shorting takes place.