What is the hash of your rig, and what coin are you mining.
You need to test different setting in your miner , if you can set the difficulty pool side extra tests can be involved, some pools I set the difficulty at the lowest and get good rates by adjusting the rate pool side, other pools I must set it at the highest setting and set it pool side to get good results, some pools that choose my difficulty based on shares ib submit it is good to choose a lower setting others its good choosing a higher setting.
Maybe if you tell us the pool and what machines you have we can better assist you