If you have the manufacturer-recommended volume, should you be designing so that your end-dimensions yield EXACTLY that recommended volume, or should you build the box as big as your max avail space, so long as you have AT LEAST that recommended volume number?

I ask only because the section on enclosure-building in the book that came with the pair of EX Series II 10" subs I just got, kind-of stops-short to a point that left me unclear.

Also, the displacement of the sub itself isn't given specifically in the book. Is there a way to calc it based on the numbers that are given? (Forgive my mathematical ignorance).