Unfortunately it is not possible to disable or change the close-out level. The requirements for this are set by our regulators and are mandatory for all retail clients to ensure that you cannot lose more than your deposited amount.
To avoid being closed out of your positions when on a margin call, you can either deposit additional funds to take your account off the margin call or you can close or reduce positions yourself.
When you're on a margin call, we'll email you to let you know. Please keep in mind that markets can move very rapidly and there's no guarantee that you'll have time to manage your position(s) before a margin close-out occurs.