I know it’s a very late answer, but if anyone comes along the same problem and reads this:
The refraction input is supposed to be a fixed value, like 1.333 for water. It’s the Index of Refraction (IOR) There are lists online about different Materials, sometimes even with different temperatures.
The Distortion will be automatically calculated by the normal of the surface. It also will be taken into account, if you put a normalmap into the material node.