Hi,
As indicated in the article link I posted, the AC overcool feature is dependent on your actual temp, your setpoint and your settings (AC overcool Max).
For example, if your ideal cooling temperature is 75 Fahrenheit, and you input a 2 Fahrenheit Overcool Maximum, it will allow your air conditioner to overcool your home to 73 Fahrenheit if the humidity preference set point has not been met.
My smartapp will just enable the firmware feature, that’s it. This is an ecobee firmware feature.
Regards.