Any smog experts out there?
This shows the relationship between AFR and emissions before the cat (or non-cat) stock type engine.
It also assumes timing is correct for the mix. (For example late timing at idle can help burn more HC, and reduce CO)
I would expect that for emissions purposes, the idle mixture targets something in the 14.1 to 14.7 AFR.
Above idle, under light load at 25 mph, probably similar will produce decent economy power and emissions.
If only NOx has increased between idle and 25 mph, I'd try to figure out what system controls the NOx rather than look at fuel mixture (which would change all combustion exhaust gases)
Just some ways to approach the issue. Don't know a lot about these new systems
There's been some timing maps posted for FI factory 318s or 360s. Maybe also some fueling maps. Those could be helpful baselines to reference.