Don't have a constraint to the top of the superview. Pin it to the bottom of the superview, and fix the height to 44, then delete the constraint linking it to the top of the view.
You achieve the pinning by selecting the view in question and using the pinning menu in interface builder (the floating menu with three icons on it, or editor-->pin from the menu bar).
To move between 3.5 and 4 inch displays, you need to link content to the correct edge of the superview. Stuff at the bottom should be stuck to the bottom.
I have written about constraint editing in interface builder here if you're interested.