If the sensor RP is not known, probing the sensor amplitude with an oscilloscope can be used set IDRIVEx.
An iterative process of adjusting the drive current setting while monitoring the signal amplitude on INAx or INBx to ground is sufficient. Simply move the sensor target to the farthest planned operating distance from the sensor, and measure the channel amplitude after the amplitude has stabilized. If the sensor amplitude is less than 1.5 VP, increase the channel IDRIVE setting. If the sensor amplitude settles to greater than 1.75 VP, decrease the channel IDRIVE setting. If there are significant differences in the sensor construction for different channels, then this process should be repeated for each channel.