There is no difference between buying more and selling short. There is no such thing as daily settlement, it should be daily profit and loss.

Market value gains and losses are for overnight positions. If you don't know the position of the order opened on the same day, you will have a mark-to-market profit and loss on the second trading day. Because futures are settled on the same day, even if they are not settled on the same day, the exchange will settle according to the settlement price of the day.