Just turn down to 2-2.5%CO, it will be fine and not lean.
The idle can be as lean as you like it will affect low speed running a bit, but is of very little effect compared to the on boost fuelling, even if .25%CO it would not harm as on boost is dictated by MAP in ECM(ECU) with regard to CTS as main factor others such as ATS are small corrective factors just for fine tuning.
As you say best to get on a ROLLING ROAD, for peace of mind.
tabetha