Actually, I'm not so sure our voltage rectifier / regulator (VRR) is a ground shunt type. Looking at the wiring diagram for our bike, I see no ground connection from the VRR.
But I do see inside the VRR diagram that there's an IC connected to three SCRs... perhaps they're using that chip to monitor system voltage, then using phase control to turn on/off the SCRs to regulate the amount of current flowing to what the system voltage calls for (low voltage, IC kicks SCRs on more often; high voltage, IC keeps SCRs off more often).