[pzhon]

A useful model to use for this type of question is one that is usually called the Independent Chip Model in the 1TT forum. One way of looking at it is that the first place is determined proportionately. Then, that player's chips are removed, and the next place is determined proportionately, etc. Another way of looking at it is that the individual chips are shuffled. Players are ranked by their highest chips.

The independent chip model says you have the following probabilities of placing in each position:

1st: 22.5%
2nd: 21.97%
3rd: 21.07%
4th: 19.22%
5th: 11.62%
6th: 3.63%

The chance to finish out of the top 4 is estimated to be 15.24%.

No one claims the ICM is exactly accurate. However, it is more consistent than simple heuristics, and it is probably much more accurate in this case.