808Mh/s takes 5.31555s to hash a nonce range.
Each block (on average) you will lose half a nonce range ... if the code is optimal - i.e. if it aborts the nonce range when an LP arrives and throws away the work - without counting it since it can't be counted.
Thus 2.65888s
Thus 0.4430% of 10 minutes
and 0.4430% of 808Mh/s is 3.58Mh/s
So the max average expected hash rate is a bit over 804MH/s
So assuming the reported number is accurate - it's not far off ...