iOS: Autolayout freeform resize with XIB

I have a problem with autolayout and autorize on iOS app. I have create a Xib (not in storyboard) with autolayout constraints and it work fine. I try to run the xib on different size simulator and, before run, I change manually in the simulated metric the size with the correct screen dimension (if I run my app on iPhone 5, I change the size in iPhone 4-inch for example). In this case the autolayout work fine, resize correctly my view and it's all ok.

The problem appear when I try to do it automatically. I set in size field the value "Freeform" and I try to run the app. In this case the app doesn't resize the view, but always display the same view with same size and doesn't change anything in front of a change about device dimension.

There is a solution for my question? Programmatically or graphically(on xib file).

Thanks