Open the Subscreen Editor. Create a new Selector 1 or Selector 2. On the rightmost tab, you'll notice that the frame is 2x2, rather than 1x1. Click the "Large" checkbox twice. The first time, nothing will happen. On the second click, the box will shrink to 1x1.
When you leave that screen and return to it, it'll appear large (2x2) again even if left at 1x1.