The min OA reduction will typically produce positive savings only if there is an existing economizer that is functioning. However, for package units we have the economizer disabled by default. We have made this decision based on the field experience of our engineers, looking into operation conditions of various package units, retrofitting package units, and doing control programming for package units. You would be surprised at the amount of packages units with economizer failure (outside air damper locked up) or economizer control not even hooked up or enabled, especially for small units.
If you are sure the economizer is working for your package units, you may enable the economizer (in the System Specifications frame) and set the economizer temperature limit to be a reasonably high value, say 72F. Doing this should produce positive electric savings, but you may have to re-calibrate the baseline model.