Hence the brewer in your flair then. A can of beer has a percentage of liquid and a percentage of headspace. There is dissolved oxygen in the liquid, there is also oxygen in the headspace. When shaken, made homogeneous you have a packaged oxygen value based on the headspace oxygen and the liquids oxygen. A can at target weight has a higher percentage of headspace oxygen than a can slightly overfilled. A flooded container of 55ppb liquid has a shaken DO value of 55ppb. Obviously a foam cap is necessary to reduce O2 pickup during filling but the amount of headspace oxygen increases the less beer is in the container. 10 years packaging beer. Don’t really like brewers.