A couple of observations. If you are running rich of peak, you want ALL
they cylinders to be rich of peak and you use the leanest, highest temp
cylinder as your guide. If you are running lean of peak, you want all
the cylinders to be lean of peak, and you use the RICHEST, highest temp
cylinder as your guide. One can see why it is good to have all they
cylinders close to each other. This is what the Gami's do.

As for carb heat. If you put on the carb heat you introduce hot air,
which is less dense. You have just richened the mixture.

As for throttle pull back. If you lean to roughness, then pull back the
throttle, you have just richened the mixture.

There is no magic. You can safely operate at high power setting rich of
peak or lean of peak. To operate lean of peak you need (or want)
EGT/CHT monitoring of all cylinders, fuel injection, Gamis and fuel
flow monitoring to REALLY do it right. You MIGHT be able to operate
lean of peak successfully with a carbureted engine, but most can't
because of uneven air and fuel distribution.

If you operate at about 50% power you can run as lean as you want
because you won't be generating enough heat to do any damage. 65% power
takes 50 degrees rich (or lean), 75% takes 100 degrees rich (or lean),
85% 150 degrees rich (or lean) etc.