Bear in mind that the drivers don't report actual temperature, only overheat warnings and errors. So the reading from the drivers sensor will be 0C under normal conditions, 100C if any driver reports an overheat warning, or 130C if any driver reports overheat shutdown.
When the drivers generate a lot of heat, some of this is passed to the MCU, so using the MCU temperature to control the fan too is useful. On one of my printers I use this:
M308 S10 y"mcutemp" a"Mcu"
M308 S11 y"drivers" a"Drivers"
M950 F2 C"fan2"
M106 P2 H10:11 T45:55 L0.3
The fan will start to come on of the MCU temperature exceeds 45C. it will be fully on of the MCU temperature exceeds 45C or if any driver reports an overheat warning.