Would a Dusk Ball's proficiency double?

Question

If I was prowling around a cave at night and decided to catch a pokemon with a Dusk Ball, would the catch rate double or just increase by the normal amount of having just one of the two circumstances?

All it says for Pokemon Black/White about the Dusk Ball is, "A somewhat different Poke Ball that makes it easier to catch wild Pokemon at night or in dark places like caves."

Answer 1

From what I know the dusk ball can either have 1x catch rate(in the day, not in a cave) or 3.5x catch rate (at night/in a cave).
There is no double bonus for cave and night.