If you have Miniaturization and research Enhanced Miniaturization, things get bigger. Example : for a medium hull and basic miniaturization, Impulse Drive Mk II takes 7 space. Immediately after researched Enhanced Miniaturization, the same medium hull and Impulse Drive Mk II takes 8 space, while neither the MK III or basic Impulse Drive changed size.
Makes Enhanced Miniaturization rather a waste of research since it's counterproductive. Now I'm going to have to look and see if Miniaturization itself made things bigger as well.