How Booster Engine Function Works?

I’m using Pixhawk 2.4.8 with ArduCopter 4.0.7 firmware and homebrew frame hexacopter.
I need to shift the maximum lift thrust to my booster engine which is at the center of the frame and the other 6 motors should stay at their minimum speed just to control the attitude and nothing else. Current consumption must be at the least possible amount.
I am using the boost function on one of the output channels and I set the boost scale to 5 (maximum) but that is not enough for me.

How can I put more load on the booster engine even more?

As I understood from experience, the flight controller would not decrease the throttle of the original motors. Do I really need to manipulate the firmware code to do so?


Sajjad - have you figured that out by now?
I also need 100% lift from the booster motor and bidirectional motors for stability only.

The issue I see with that is torque control. Stopping the copter from rotating in the opposite direction to the rotation of the main rotor.