Earnings calculators show you what you'd make in an ideal environment. Mining is anything but an ideal environment. You might want to take a look at the pool's official thread to understand their payout method. Also, you need to understand that your share of the coins is very much dependent upon your accepted contributions during shifts and how the pool as a whole is doing luck-wise.
over the long run it shouldnt be question of luck. but the ideal count give me 2x more, that makes me suspecting. didnt say its pool. can it internet connection or something else