How exactly does “arranged financing” work?

Prime brokers offer what is called "arranged financing" which allows hedge funds to gain maximum leverage - more than allowed under the Portfolio Financing platform. I understand there is an element of stock lending where some or most of the Hedge Fund's long/short securities in the account are being transferred (lent out) to another legal entity (usually offshore), which leaves only a fraction of the portfolio in the main account, where a 15% HC is applied. The rest of the portfolio is collateralized as a stock loan.... I am just missing the exact details of how and what is trasfered and how is the additional leverage achieved? Thank you