The payouts wobble - sometimes severely and sometimes down to zero but in the longer term (not just looking at a few blocks) you'll get the right total payout.
I think the only way to explain this is to look at how much you've received. Lets look at the last 24 hours as an example.
Looking at the block explorer (which uses UTC) for the last 24 hours, from 1AM yesterday 1AM today, you've received a total of 1974568.17745222 IFC at your iC6Yr743UWVzt3vtYWBXGxPsZNBmUzjgNB address . 706000 IFC of this was a big lump-sum so we'll deduct that as it wouldn't have come from the pool (it's a good idea to use a unique address for the pool to make checking like this easier). Anyway, that leaves
1268568.17745222 that you have received from the pool on your iC6Yr743UWVzt3vtYWBXGxPsZNBmUzjgNB address over the last 24 hours.
The average (mean) hashing speed of your iC6Yr743UWVzt3vtYWBXGxPsZNBmUzjgNB address over the last 24 hours, as shown on the graph below was 991kh/s.
The average network difficulty of Infinitecoin from 1AM UTC yesterday to 1AM UTC today was 2.925633059 (average of infinitecoin blocks 206911 to 209826 which you can confirm by the block explorer and a spreadsheet).
So, at an average difficulty of 2.925633059 and an average hashrate of 991 kh/s, how much should you have earned?
I don't know of a specific IFC calculator but we can interpolate from burnside's LTC calculator at
http://ltc.kattare.com/calc.php.
According to burnside's LTC calculator you would expect to earn 340.7044 LTC per day on average. At Litecoin's rate of 50 LTC per block, that's 6.814088 blocks (ie 340.7044 / 50 ) of difficulty 2.925633059 that you'd expect to find on average. At Infinitecoin's 131072 IFC per block, 6.814088 blocksworth =
893136.142336 IFC that you'd be expected to mine at your average hashrate of 991 kh/s.
Seeing as you've actually received 1268568.17745222 IFC from the pool, you've received 142% of what would be expected.
Seems good to me