Weblogic 12C min thread pool size

Hi. I am an integration developer in a big company. We are using Osb12.2.1.2. I was wondering about the "Self Tuning Thread Minimum Pool Size" configuration. It's now set to 1 and the max is 400. The "Enable Native IO" is set to true. But when I look on the monitoring screen, I see that the "Total Execute Threads" is 123. I waited 2-3 minutes and checked again, still 123. I expected to see a smaller number, because the minimum threads is set to 1 so Weblogic needs to shrink when thread is closed... am I wrong?

My original thinking was to increase the "Self Tuning Thread Minimum Pool Size" from 1 to 200. I thought it will give us a better performance…