the pool has low net hashrate, so lower chance to get a block... then if you are unsure, you can check all the block you mined and do the full calculation (and see where it goes) rather than doing speculations...

i'm mining on supernova which has 50% of the net hash, how is this a small pool?

Guys , which speed gtx970 reaches on decred, I can't find such statistics...

lol thought you were mining on yiimp, since you were complaining here

ah... you think that he was lucky?

on a large pool, only large miner gets "normal" payout, small miner may not get shares for every block which are found, reducing a bit the income (well on suprnova you can choose your diff though), scaling might differ a bit between small and larger miner etc...
however there is a smaller risk involved by using large pool than small one (as for small pool, you need to run a longer time before finding a block...)

on suprnova, 1 or 4 on the longpoll from my first tests

No it's not. The bigger the pool, the closer to estimated income you'll get, since you'll find blocks more often. You can look at this under the 'blocks' tab and then look at the %. If it's above 100% then the pool has been having problems finding blocks and you'll receive a reduced income, if it's below 100 you'll receive more then the estimate.

As with most stats, the more data points you have, the closer it'll reflect estimates and the more accurate estimates will be. This is why people generally all mine on bigger pools, it's more static income and less random 'luck'. Faster block times can also help with this sort of thing... But there are problems with doing that.

Generally speaking look for a pool with a 24hr luck that is around 100%. If it's 20% higher or lower then that, it's generally not worth mining on. I personally don't mine on pools with less then 5% of the network hashrate as well as the RNG is way too high (although that depends on block time for the coin).

This is putting aside that pools seem to have been having problems with stratum support. It seems like the stratums are screwed up compared to using normal getwork without stratum. I've found normal getwork works better for this coin. Your hashrate usually does not fluctuate at all.

One thing came to my mind, if you have set really low auto payout treshold then relatively high tx fees eat 4 x 0.05= 0.2 DCR from your daily earnings.