Just like so many things, there are multiple processes that work. My 5500 has a 9 gallon DEF tank and when I bought the truck. I asked my Ram dealership service writer of 20 years, anything I should do special with DEF, and answer was: " Top of at half full, and you'll be fine." And so, for nearly 5 years, and living in the South where we have 40+ 100°F days a year and maybe two weeks of mild winter, it has worked for me. And, when I had last surgery in 2019, truck sat barely used almost a year. So with all that, I gleam out of it: buy the freshest DEF you can and follow the fill interval that works for you. Oh, BTW, I purchased a DEF spectrum analyzer a couple years ago I've used once to see how it works.
Cheers, Ron