No one will buy stock and borrowing stock at the same time...

No one will buy stock and borrowing stock at the same time unless he want to control the announcement of holding position and manipulate price.
6% is enough for short selling base on the liquidity of this stock and no need to borrow anymore. And they bough quit a lot of shares in the open market during last two weeks. Large proportion of the huge volume coming from them.
Short time no idea how they are going to manipulate the price. But medium time they want more stocks for sure otherwise they don't need to borrow.