It depends greatly on the pool and the day. Somedays I average above for the 24hrs and some days under.
Nanopool is far more stable and always the same or higher hashrate 24hr average.
Hashvault ok and cryptoknight.cc pool always less.
There are soo many factors. Look at the average over several days
It is not about the pool or the day
If after 2 weeks pool show that one rig has total of 14000000000 hashes and other ones have 13000000000 or even 11000000000, it means that some machines are hashing less than the others, and all of them are 6xVega with 12000H/s
It happens on supportxmr, it happens on nanopool, it happens on many others
I am not saying that somebody is stealing the hashes, because some machines are hashing well, but there must be some hardware or software difference that affects the miner or data sent by miner, simply because SRB and CAST have this issue and STAK doesn't