With Fixed Lot/Unit the Slave trade size is fixed and is defined in advance for each trade no matter the Equity, Balance or Free Margin of both Slave and Master accounts
When using the Fixed Lot or Fixed Unit method, whatever the Master trade size is, each trade placed on the Slave account will be the defined Fixed lot or Fixed Unit value, no matter the Equity, Balance, or Free Margin of both Slave and Master accounts.

Please note that if you are using a broker account configured with a mini, micro, or standard lot, setting a "Fixed Lots" with a value of 1, will open respectively 1 mini, 1 micro, or 1 standard lot.

Difference between Lot and Units
100,000 units represent the equivalent of 1 standard lot with a notional value of 100,000 USD, so for example, if you set the Fixed Units to 20,000 this is equivalent to 0.2 standard lot.

Examples: