Trying to figure out best operation!

  if (mid_reading > 0){
   left_motor=map((mid_reading*100), 0, 100, 0 , 127.5);
  analogWrite (5,left_motor); 
  right_motor= map ((mid_reading*100),0,100,0,127.5);
    analogWrite(6,right_motor); }
else if
     left_motor= map((left_reading*100),0,100,0,255);
  analogWrite(6, right_motor); 
   right_motor= map((right_reading*100),0,100,0,255);
    analogWrite(5, left_motor); }

This is currently what I'm using. Essentially for operation I want it so the middle sensor (mid_reading) will drive the motors to half power. The left sensor will control the right motor and vice versa. I want it so when the middle sensor is all the way on both motors will be at half but if it receives input from either the right or left I want the motors to drive faster. What is the best way to achieve this?

#define LEFT    5
#define RIGHT   6

    analogWrite (LEFT,  map ((mid_reading + right_reading) * 50),0,100,0,255);
    analogWrite (RIGHT, map ((mid_reading + left_reading)  * 50),0,100,0,255);