The design of heated grips has changed. Originally BMW used 2 position control with the 1/2 heat position merely adding a length of resistor wire in series with the grip elements. That wire was traditionally orange and sat in the electrical connection box. In certain fault conditions it was known to cause damage to wiring harnesses as it warmed up and melted insulation of other wiring around it. These older systems were simple and basic, no electronics and full heat is dependent on the resistance of the grip heater element.
Later systems wired through the control ECU's are more sophisticated with multiple settings and they use what some will call PWM, (Pulse Width Modulation). Basically it means the power to the grip elements is turned on and off at a fixed frequency with the width of the on pulse increasing for increased heat. The efficiency of these systems is dependent on the quality of the components used and how well the circuit is designed. On a well designed controller with high quality components the hottest position should be 100% on and somewhere above 95% efficient, from there it is a matter of the resistance of the grip elements determining the current and hence the highest heat.
How good the BMW circuits are, I cant tell you as I have never had the chance to look at any BMW circuit boards, I know the fully variable controllers I have on my own machines are up around 99% efficient and do give the full range of 0 to 100% to the grip elements but then they are not a commercially available controller
