The rear brakes engage at about 20% force as the front. That said, the difference between front and back is dynamic and somewhat more complex, and the ABS controls the wheels from stopping rotation to prevent skidding.
If you want to save fuel and $$, drive so the discs/rotors don't heat up much! Drive as if you were barefoot and thumbtacks were stuck on the brake pedal.
I get around 4L / 100km on average (around 60mpg / US) and the way I drive the rotors are cold when I park the car. If I would heat the brakes any more than absolutely necessary, I would be wasting fuel!
You may want to look at:
https://www.ecomodder.com/forum/EM-h...ecodriving.php