I plug in my hashrate on coinwarz and use the calculator there. my hashrate is just over 1900, but I plug in 1800 on coinwarz to try and be conservative.
at 1800 according to coinwarz I should be averaging 727, keep in mind I used 1800 not 1900+. and 1200 in 4 hours is quite low comparitively to the 2900 that the calculator is telling me.  Also when I look at the list of found blocks most of them have been pretty decent a couple of lows but also a lot of highs.