A narrowband sensor will tell you if the ratio your running is making the engine happy. I had the benefit of running both a narrow and wide band sensor at the same time. I found the ratios my engine liked were dynamic... Generally richer below tq peak rpm, and leaning as rpm would rise.
A narrow band sensor will not have any "true" value as a ratio indicator, only as a "happy" monitor.
As an example, lets say I'm running the engine at a wide band confirmed 12:1 ratio. I look at the data logs, and look at the narrow band output voltage. If you see amplitude spikes(high/low) the engine wants something different. Add some fuel, log it, than look at the amplitude again. If the voltage line is smoother, keep moving in that direction. If its worse, go the other way. A smooth output voltage line is the goal. Just ignore any other part of the info you get from this. voltage value is of no value with a narrow band outside of 14.64:1 ratios.
Bottom line.. A wideband will tell you where you are. A narrow band will tell you if you should be there!