It works like this:

A bounty is 1000 coins. If there is one person with one stake, he will get all the coins. If there are two people with one stake each, they will get 500 each. And so on. Bounty pool divided by total stakes gathered by participants times your stakes is how much coins you will get.

(pool / total stakes gathered by everyone) * your stakes = your coins

In the above example with 1000 coins and two people with 1 stake each:
(1000 / 2) * 1 = 500