Fair enough. Keep working on it then. I just didn't want to tell you to keep tweaking if you were satisfied.

When catalytic converters were first added, they controlled the NOx. The high NOx at idle was in part due to the leaner idle mixes introduced to bring down the CO and HC. Idle speeds were increased, and idle stop solenoids solved the run on from hot chamber and wider idle throttle opening. My understanding is that with controlled EFI, idle mixes close to stoich continued to be the norm.

Here's a post by Tuner with graph plotting Combustion products vs. AFR. As he explains, even on stock engines idle mixes tended to be much richer than stoich until emmissions concerns started pushing them leaner.

The other thing that will make an engine a little hotter is retarded timing. On my fully smogged '85 AMC 360, there is a coolant temperature switch to provide the distributor's vacuum advance full manifold vacuum if coolant hit 220 degrees F. Cold, the vacuum advance gets a mix of ported and manifold vacuum. At normal operating temperatures, it gets ported only.
So this shows that timing was signficant enough effect on coolant temperature that the OEMs used it when emmissions and drivability got really tricky to balance.

Back to idle fuel mixes. The research from performance oriented (non-emmissions) testing appears to favor richer than stoich at idle. See
the AFR vs. Load graphs published by Larew,Taylor and Obert. They're posted in this thread AFR Characteristics vs. Load. It is worth a looking at even though the thread got a little jumbled when the threads were merged.