sub box size

That is correct. Also, when it's too big, the bass becomes sloppy. There is no control over the woofer motion. When it's too small, you'll lose low end response. The bass becomes peaky in the mid-bass region and you have no definition in the lower sub-bass region. You can correct for this if you shelf the woofer. Shelving the woofer consists of adding equalization in the lower sub frequencies and having lots of power to force out the low sub-bass notes. If you decide to use shelving, I would suggest a 2 to 1 power ratio. Use an amp with about twice as much RMS power as the RMS rating of the woofer. Also, make sure the box is completely sealed and has absolutely no leaks. A leaky box means less bass output (due to cancellation) and lower power handling. It works, but you may have some adverse effects. You will still have the peaks in the mid-bass region, which you can effectively filter out by lowering the xover point, plus you may blow the woofer from overpowering it. I would simply suggest to build the right size box for the woofer you are using.