If you take the same sub out of the box and push on it, it will return to the rest point immediately. Same thing in a box that's .1cu or one that's 100cu, it doesn't matter. The way you describe it just means that your enclosure is leaking.The easiest thing for you to do, is take a subwoofer, make a super small enclosure and one that is considerably larger. Install said sub in each. Press the cone down. Then tell me which one returns to its rest point faster. This right here will show you the smaller the box, the more the air spring works. Which controls the diaphragm by pushing or pulling it.