As you describe, the distance from the neck flange to the opening of your bottle (ie, the hole where the fizzy goodness comes out) is less than 1.6cm, so it will be fine.
It's probably worth pointing out that the people who make the rules have actually seen soda bottles before. So yes, there are measurements (because there's always someone that tries to do something weird) but they are written so that you can go to your supermarket and by a normal 1L plastic bottle of major-manufacturer soda, and have something that works.