Stoich is still 14.7, thats still the "chemically correct" mixture.

But that would be too hot a burn, so is no use, and would not give good power, so is no use.

12.5/12.6 is the point of peak power, this is what you want to be running if you are able to without heat issues, on a YB though, high 11s is as close as most people go for safety reasons.