Is this "new Math" coming back again???...lol...lol.
20:1 mix is 6.4 ounces of oil...40:1 mix is 3.2 ounces of oil...Where do you get that 20:1 is leaner on oil than 40:1???...lol....You have double the oil at 20:1...NOT at 40:1...lol.
Guess I didnt specify clearly which mixture. There is less gasoline in a higher(lower#) mix. This may or may not make a substantial difference in most cases and in certain instances more oil might be a good idea.. However in a well tuned build with a carefully jetted carb its noticeable. It will usually affect low to mid range, especially with carbs with a low speed circuit/pilot jet.
My Athena Mina is closely jetted. I have lowered the pilot # to an optimum mixture for clean running and good response.
Drops in temps will greatly affect it, as its jetted in the 70-80s. Gets hotter the mixture richens, colder it leans.
Where I live we have large swings almost weekly. I discovered that a 40:1 mix(normal is 50:1) leaned it just enough for
it to run as normal at reasonably lower temps. I use 40:1 in the colder months, 50:1 in the hotter months.
Also ratios are for oil poured into a gallon of gas. If one has a marked true gallon container and pours the oil in first then fills to a gallon mark, the mixture is leaner still. In your case you would have only 121.6 oz of fuel.
I know folks in the forum are too smart for this!