There is no sensitivity adjustment. The ABS depends on inputs from each wheel speed sensor to determine that it needs to pulse one or more wheels.
I'm assuming that you're feeling some kind of pulse in the pedal most of the time (80% by your estimate if I read correctly), which is why you're assuming that it's the ABS pulse.
It might be an errant wheel speed sensor, but I'd pull the wheels, check pad condition, and measure rotor runout to make sure that what you're feeling is an ABS pulse as opposed to a rotor with thickness variation.
BTW - Welcome to DC!
PS - I lived in Dallas, GA from 1989 - 1992! It sure has grown - it was still a pretty sleepy little place when we left for Illinois.