It won't jump up & down because i'm not using score-based system, that's why i'm not showing "estimated reward".
Excuse me, but jumps in estimated reward are not related to score system. It's changing also in share based system for miners with slow submit rate, because in formula user_shares / total_shares * 50, 'total shares' is rising constantly, but 'user shares' is changing only time to time.
Sorry, that wasn't some kind of offence to your system.
In my experience standart deviation of estimated reward in score-based pool was higher than in share-based. I know that it averages out and the reward will be the same over time.