Launch your second gui as:
hFig2 = SecondGUI;
set( hFig2, 'Position', [x y width height] );
where [x y width height] are whatever you want them to be taken from the GUI that is launching the second GUI.
You can get the current GUI's position using it's tag as e.g.
If you prefer you can pass position as an argument when you launch your second GUI:
hFig2 = SecondGUI( 'Position', [x y width height] );