Patterson only states how much liquid (Liquid nitrogen for all they care) it takes to cover one of their 35mm reels and 120 reels. They aren't the developer/fixer manufacturers and therefore don't address this issue. If you ever look with the top off how much 295ml is, with the reel in there, it barely covers it, and i personally would at least just go to 350ml to be safe (one of the reasons i went to 400ml)
As to the reason behind stating minimum amount of developer
KODAK states this is the minimum amount of developer per roll that you will ever need. So if you develop say 36 scenes that are pure white (maybe a small black dot somewhere, idk) and you use less than minimum amount of developer needed, you are still within safety margins. Me using less than stated half of minimum, would probably get gray negatives. And so, this minimum, is Kodaks insurance, so that no one can come back and say, hey, your d76 sucks, and doesn't develop fully. With the minimum amount of d76, this would be user error.