system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why filling a cup at the soda machine the fizz doesn’t overflow but when filling a cup from a 2 liter the fizz is very volatile and over flows easily and both drinks taste like the same carbonation level.

Wow so many different answers to this question and a lot sound like they could possibly be correct. So tonight I’m going to test the cold beverage theory. Will poring cold soda into my tumbler full of ice result in less fizz bubbles. Up until now I’ve only pored warm soda into the ice fill receptacle. 

I will also test the suggestion to used watery ice instead of the cold dry ice right out of the freezer. Will the watery warmer ice result in less fizz. I will use my warm soda along with watery ice to see if I get a different result.
gpt
Because the soda you get form a machine isn’t quite the same as the soda from the bottle.

Restaurants get packs of the soda syrup that they hook up to the machine, which the machine then mixes with water and adds the carbonation right then and there as you push the lever.  This means that the carbonation is less throughly mixed/dissolved in the soda. There is less carbonation in soda from the machine than bottled soda.