Gary, That's my understanding as well.
On-exchange shorting is generally regulated (margin caps), so that is typically capped at a 2:1 leverage and limited by one having to have 50% of the short value as margin deposit/collateral.
Off-exchange shorting is the synthetic contract/options, so that has high/potentially unlimited leverage. The actual leverage and margin deposit is a negotiation between the client and the Market Maker, subject to less stringent regulations.