That is more broker/clearing firm dependent than the size of the customer. When I was a broker dealer/market maker, I received most of the credit and my clearing firm only kept a portion of it.
Reminder: When you buy on margin you pay interest on the money you borrow. When you sell short you don't pay interest on securities that are easy to borrow to execute the short.
Nice try Robert but you could have just as easily said it's a shame you don't feel like you can use the search function on you brokers website to answer these questions. You very well know people come here to start conversations and gain knowledge and our clients don't need to negotiate to get short sale proceeds and interest. But I guess having information readily available and easy to find via a search box is something new to some brokers. IB has all this info on our site and even has a calculator to help one calculate interest on short sale proceeds. Unfortunately in this low interest rate environment we don't pay much or anything until the value of proceeds exceeds $2mm. Rates can be found here: https://www.interactivebrokers.com/en/index.php?f=1595&p=secfinancing However, the low payment on proceeds is offset by our margin rates which start at 2.59% and slide down to 1.39%. (For comparison sake, according to your site your rates start at 7.75% sliding down to a a low of 5.25.% as of 3/3/20 ). OP, while your question has largely been answered, here's a pretty good write-up on short sale proceeds that should answer your questions as well as provide examples: https://ibkr.info/article/41