Remember, all widebands read lambda. To give an AFR number, the lambda value is just converted to AFR using a math formula. So, it doesn't really matter what "ideal" or lambda =1 AFR is picked as ideal as long as you stick with it from wideband setup through logging to any fueling calculations. In theory, you can tune E85 using 14.7 as the ideal AFR if you wanted to.
Now, using lambda does make it clearer because you're always working with ratios which correctly represent the fueling. 1.0 is the ideal mixture. 0.9 is decent for PE mode. 1.1 could be used for lean cruise.