Domicile master radio button
The domicile master is the planet that is the domicile lord of the sect light in charge, or if you follow Rhetorius, the confine lord of the sect light. In the case that you switch the predomination, the other becomes the joint domicile master. Schmidt says that this planet is supposed to represent the destination of the native.
Predomination is a tricky issue that involves sect and the horizonal placement of the lights (whether the Sun/Moon is cadent, succeedent, or angular). This setting will affect the Universal Hermetics Report.