You don't understand, it depends on what direction you are doing. It is not that the margin will be increased if it falls, but that it needs to be increased because the margin is insufficient. Why does it lead to insufficient margin? It is because of your floating loss minus the money in your account that your net worth can't meet the minimum maintenance margin requirement (that is, you are almost insolvent and almost lost all your book funds). In other words, because of the large floating losses, it is necessary to add a deposit. Therefore, do more (buy up), then you will earn if you go up, and you will lose if you fall. So if it falls too much, you may need to add a margin, of course not. Similarly, if you short (buy down), you will make money if you fall, and lose money if you rise, so you may need to add margin if you rise.