True, headroom is a good thing. But keep in mind with a sealed subwoofer, the enclosure will ultimately determine the speaker's power handling ability. If your enclosure is smaller than optimal, the sub will take more power to get going. If you box is larger than optimal, the sub will have a slightly bloated low end and will bottom out on much less power.

You guys both probably have slightly undersized enclosures (which is not a bad thing). A little polyfill helps the frequency response in that situation so try adding some. Usually 1 pound per cubic foot is a good ratio.

 

I know that mine is. Internal volume is listed at .7 cube and the 10" CVR needs .8 I also found a 1 lb bag of poly-fill at wally world for 3 bucks and was able to stuff about half a bag into my box without packing it too tightly.