Thanks for your answer.
Let me clarify my question. My variables are as following:

I have the possibility of having 18 runs. I could set user specified to 18 or I could change the "Number of Replicate Runs" to 4 which result in 18 runs. Here are the result of both approach:
Specifying 18 in "user specified" field:

change the "Number of Replicate Runs" to 4:

Could you please let me know how to decide based on these results.
Thanks!