Every engine is different and it depends on the inlet runner design and how fast they warm up to a temperature that atomises the fuel correctly so we dont have to literally waste it to get enough in the actual cylinder. Cams and headwork tend to make this problem much worse as lower gas speed does not bode well with cold runners and fuel that doesnt atomise properly.

Aim to get as close to stoich that the engine design will allow, but on most engines you are likely to be running between 12.5 and 13.5:1