Try adding space between searchbox and popup menu

[anonimeact]

Hi, i try to add space between the searchbox and popup menu by add custom positionCalback like this, and not working.

return RelativeRect.fromSize(
      Rect.fromPoints(
        popupButtonObject.localToGlobal(popupButtonObject.size.bottomLeft(Offset(0, 20)), ancestor: overlay),
        popupButtonObject.localToGlobal(popupButtonObject.size.bottomRight(Offset.zero), ancestor: overlay),
      ),
      Size(overlay.size.width, overlay.size.height),
    );

but when i try changing 20 with negative value (e.g: -20), the popupmenu go up, Is there any suggestion regarding my confusion?