I am trying to set a fixed Y-coordinate position (read top-to-bottom) regardless of what look and feel is being used. Since LAFs are not consistent in their component sizes, the width and height of the JPanel may differ, and on GridBagLayout, the central position of the JPanel mostly increases in overall dimensions.
Reducing the dimensions can have a bad effect on the components in various LAFs (which could've been a solution if that wasn't the case) as they were not originally meant to be compressed to a more narrow height.
The base references are Windows and Windows Classic LAFs, both of which are at the same Y position.
A simple picture says what needs to be accomplish for all without hard-coding a static value that will stop working properly once a different system font used by the LAF (Linux being an example) comes into play.