Hi Shallowgas,
The pool uses a PPLNS reward system. Simply put it pays based on the number of shares you submit over a period of time.
To illustrate this take the example of D99erPFYxti2gcT7xTQNgTRrdUtguh7Qka. They started mining on the pool a couple days before you joined. His portion of submitted shares is much greater because of this. Over time your portion of submitted shares will outnumber his (due to your higher hash rate) and your payout will increase accordingly.
Here is a charts showing your payout increasing as your portion of submitted shares increase:
![](https://ip.bitcointalk.org/?u=https%3A%2F%2Fi.imgur.com%2FFPIrwoJ.png&t=663&c=oCOSrVmWa46Tvw)
Another miner with 1.5 Mh/s started shortly after you did so they are also increasing their number of submitted shares along with you but at a slightly higher rate due to his higher level of submitted shares:
![](https://ip.bitcointalk.org/?u=https%3A%2F%2Fi.imgur.com%2Fk7GUXHS.png&t=663&c=bwFuHyDYP_rR1w)
The effect of both of you starting to submit shares is decreasing the % of shares D99erPFYxti2gcT7xTQNgTRrdUtguh7Qka is providing. The reason his payout is still higher than yours is because of the two days of work he has submitted before you came on board:
![](https://ip.bitcointalk.org/?u=https%3A%2F%2Fi.imgur.com%2FZpXZt3o.png&t=663&c=RTOVdFMJhO0rBQ)
You will notice that if you completely stop mining the pool you will continue to get payouts for a couple of days because of the submitted shares you are currently contributing.
Look at DTWPTRSi9HoLh69NPd2fbDWUGHrx1nLdmk for an example of this. He has not been mining for a little while but will continue to get (decreasing) payouts because of the work submitted while he was on the pool.
I hope this illustrates how the payout system works. If you like I can provide links to much more in-depth explanations.