Never trust narrowband voltages, they are showing weather on Mars. The only thing they are good for - indicating 14.7:1, and that's it. Anything off - and they can show whatever they feel like at given moment.
You can make some very ballpark-ish presumptions about your actual AFRs based on EGTs and ignition angle + ignition retard (CFs), but if you have a wideband - just look at it. Anything between 11.5-12.5 when stepping on it should generally be fine.
EDIT: AFRs I quoted are for a pure gasoline, without w/m injection.