Interesting, is that a measured hash rate, or the reported hash rate? There are two possibilities for this difference
1. I messed up the launch params on hawaii archs, in which case you may be able to fix it with where k is some value > 0, and is 8 by default.
2. There's too much variance in the reported hashrate, and it needs to be averaged by the miner over a longer period of time (which I'll probably add in the next release, because my reported rates are all over the place sometimes too.)