Quoted from unigroove:The same goes for the "almost guaranteed" multiball on the third ball on many games. If you get it every time, it is less fun than having to actually achieve something (aside from making 1 shot) to get a multiball as a reward.
This is precisely why I changed the default in Data East Star Wars v.1.04 to not hand you multi-ball on the third ball (or in this case, Tri-ball).