Radio button and checkbox - reduce bounding box size

Two thoughts, You could put an invisible shape over the boxes that would prevent them from being clicked. Then put small invisible shapes over each button that could be clicked on. That may be a lot easier than building the buttons from scratch. Alternatively, you could replace the buttons with copies of them that do not have the too-large border.

The point is, that however you do it, if you use states named Selected and Normal, you will get those behaviors without having to write your own triggers. Select the appropriate group of buttons, right click, and make them a button set, and you will have all the exact same behaviors as the built-in buttons.

And no, it is not you; the built-in borders on radio and check buttons are unreasonable oversized.