Am not familiar with the details of cashflows.
If my account has 100cash, long 200 stocks, short 100stocks. I incur interest cost although cash shown is 0 as the 100 margin for long is separate from the short proceeds and are charged at a +spread while short proceeds a - spread.
How about if 100cash, long200 stocks, short 100options? The option proceeds is cash into the account to directly offset the long borrowing(ignore settlement lag)? So I don't incur interest cost?