How often to use a minigame?

[Jubal]

So, some of you may've seen the asteroids trailer I posted. I've currently got the minigame triggering any time a player goes between worlds, on a 20% chance. Do people think this is about right, or should it be more/less common? Only having it on certain missions may well be an option, and would "relax" the gameplay experience a bit for players who don't want to be on the edge of their seat whilst making the hyperspace jumps. I sort of like the idea of having it forecasted, but making a player stay longer on a particular world to avoid the asteroid fields might get annoying. Thoughts appreciated!