Hard to say what values works best here is why.
You have to forget AFR ratio and use Lambda.
Again the Narrow band sensors are only accurate at Lambda 1 and that is what the computers will try and achieve regardless of the fuel type.
Having the Stoich value match fuel used makes the math work and minimizes fuel trimming.
Talking and using AFR is just plain confusing unless you are working with pure gasoline, then you can say 14.7 is target or 15.1 is optimum MPG. etc.
Go back and look at the chart I posted, you can see AFR changes but all Equal Lambda 1.
maybe you need to target 1.01 or 1.02 but don't know how you would force the computer to do that?
Maybe Just Maybe this is how Chrysler uses Stoich?
We can only assume how the OEMs use the Stoich ratio, either to target or to offset from Lambda 1
Maybe someone smarter than me can chime in with some hardcore facts.
I have seen that GM Ford and Chrysler all handle it differently to some extent.
Ford uses Wide bands starting somewhere around 2011, instead of narrow bands which changes how they use the Stoich value also.
On most cars I have been successful tuning on gasoline E10 14.10 Stoich then changing to MS109 with only changing the Stoich value to 13.40, and maintaining same LTFT and WOT Lambda.
Also working with Flex fuel sensors and E-fuels, automatically reads E content and populates the Stoich value via the table above.