It's just a math problem. To see if ice paradox is worth using, you need to see what your average potency per second is in fire phase for a given action. If ice paradox's potency per second is greater than an average fire action, it's worth using. I didn't math it out but right now the recommended ice phase is blizzard 3, blizzard 4, ice paradox, transpose, fire 3 firestarter proc.
They wouldn't recommend this unless ice paradox has higher average pps versus fire actions.