freqtrade_origin/docs/leverage.md

For shorts, the currency which pays the interest fee for the borrowed currency is purchased at the same time of the closing trade (This means that the amount purchased in short closing trades is greater than the amount sold in short opening trades).

For longs, the currency which pays the interest fee for the borrowed will already be owned by the user and does not need to be purchased. The interest is subtracted from the close_value of the trade.