Make sure you had a look at how shares are being produced.

There are big differences in hashing power of different miners. To optimize network traffic between your miners and the pool we have introduced the variable difficulty algorithm (or vardiff). It assigns more difficult tasks to stronger miners (higher difficulty) and easier tasks to weaker miners so that an average communication frequency is roughly the same for all miners.

Vardiff assigns a quantity of work to each miner such that it should send results back to the pool 16 to 20 times per minute. Why 16-20 times? According to our measurements, this is the ideal frequency that allows a balanced data load to our servers and correct measurements of your miner's hash rate.

If your miner is too fast, Vardiff increases the difficulty for its work. When too slow, the difficulty decreases.

For example, a difficulty of 20 means that you will find 20 times less hashes satisfying the requirement, but you will be given 20 shares per each submission. Hence you will not lose any shares and the network does not get jammed.