The payout is based on the effective hashrate which is calculated from valid shares/accepted hashes, so it's not based on the miner's current hashrate nor reported hashrate.
It also depends on the payment methods which is chosen by a miner (PPS or PPLNS).
So it really is. It is for this reason that we must look at the real power that your farm gives out. Now, due to rising prices, we see that all calculators work approximately.