Mirror Master Risk allows you to adjust the risk your account will take when auto-copying another user.
If you auto-copy another account and set the Amount to Mirror at 1.0, your account would copy trades with the SAME risk taken by the master Signal. e.g:
If you had £10,000, copying a signal with £1,000 on account. If the Signal placed a trade of 0.01 lots you would copy at 0.1 lots. Your account size is 10x larger - therefore your trade size will be to match the risk.
If you changed your amount to mirror to 2.0. Using the same example your lot size would be double the Signals e.g. 0.2 lots. You are therefore INCREASING your exposure.
If you entered 0.5, your lot size would be half 0.05 lots. In this instance you are DECREASING your exposure.