First, R9 is responsible for decreasing sensitivity. Lower the resistance in R9 to lower the sensitivity.
Second, forcing "ignore" to 500 millivolts can be accomplished by making a voltage divider that sets pin 3 at 500 millivolts above pin 2.
Third hysteresis is accomplished by adding a resistor from the output to the non-inverting input (pin 3).
The bias circuit for "ignore" will contribute to reducing the sensitivity by wasting some of the signal.
These things are interactive. I could not do the math from here.