I thought that rising rate regulators were only for people who wanted to use undersized injectors, so that they retain good idle, and increase the pressure on boost to get adequate fuel volume??

Regular EFI/Turbo cars have a high pressure regulator, but they aren't rising rate. Although if my memory serves me correctly there are 2 pressure settings on the stock CA18 fuel pressure regulator. Primarily to improve starting performance of a hot engine.

The CA18 Fuel pressure regulator is controlled by a solenoid which is controlled by manifold pressure and the ECU. The ECU takes information from the ignition switch, air flow meter, temperature sensor, and crank angle sensor to figure out what pressure is required.

This is described in the S13 Silvia Factory Manual, on page EF&EC-20.

If anyone can enlighten me more, then great.