Enabling internal pullup resistors in the ATtiny85 not only takes care of proper biasing of the comparator pins, but also helps reduce current consumption when the ATtiny85 is put to sleep.

A 9-bit ADC referenced to 10V full-scale has a least significant bit of 19.5 mV. The hysteresis voltage is 22.6 mV, and this dead zone equates to more than a least significant bit for a 9-bit ADC, so ...