@User: There is no such thing in SPICE as a 3-terminal MOSFET. The 3-terminal device is a simplification in xschem where the 4th terminal is declared as a property of the device, instead of being a wire. This allows schematics to be much less cluttered with wires since everyone knows that most devices will have the bulk terminal tied to a power rail. In all cases (both xschem and magic) the device will be extracted as a four-terminal device. Magic will infer the bulk terminal connection from any substrate tap in the layout (which does not have to be close to the device, because that is only a DRC consideration for magic, not an extraction consideration).