Dragging forms on iOS

I can’t tell what settings allow my forms to be dragged horizontally on my iPhone 6s. My project has about 25 non-modal forms in it - all designed for portrait mode. Some of them allow me to drag them left or right and some don’t (after dragging them they return close to the proper position) - all of my non-modal forms allow me to drag them vertically. Can anyone tell me what setting causes this (ie. what allows some forms to be dragged and others not)?