How appium 1.7.1 , xocde 9 run multiple ios simulators?

Hello, all
I am using appium , recently it’s upgrade to 1.7.1 and xcode to 9.
The good news is xcode can run several simulators at the same time, and it is said that appium 1.7.1 can accept several connections to run several simulators with one appium instance. Is that true? I hope I can find some technical information or guide from official way. Because I can not make it true .

Here is my scenario:
I create two simulators iPhone 5s , iPhone 6s
when I run test cases in 5s first, of course , it can run well . During the case’s running time, I run test cases in 6s, I can see, some actions (like install app) run in 6s correctly, but after that , all remain actions (like click button) migrate to 5s, which confuse the whole test cases running.
I guess that although I set different wdalocalport (5s 8020,6s 8010), but the webdriveragent(8100) can only communicate with one port at the same time.
How can I set start parameters in start up process?