Reducing the size to 1 I don't think is the "correct" solution.
In the inspector for the containers look for the "mouse" tab. That determines how the mouse interacts with that control. By default it is on STOP. Meaning it blocks all inputs "behind" it in your scene. You probably should change it to pass or ignore.
Imaging you have a complex ui with multiple layers of buttons. You only want the top one to register click events, so it would be on STOP. If you did IGNORE then the top button would not register click events, bit the buttons under it would. If you had on PASS the top button registers the click, but then passes on the click event to the buttons under it.
Right now you still have a 1px dead zone.
Hope that helps.
