Normally I'd be inclined to agree, hence my not investigating this until now, but in the case of these KEFs, they provide specs for an enclosure to provide the best sound. The ones I installed the other day were free air and sounded awesome. Well, like awesome sounding ceiling speakers. I'm very curious about the difference with the enclosure.

The enclosure they are specifying is very large I could put two 12" subs in a 2cuft box if I were doing this in my car. So my thinking is they've created a design which works well in an IB install, but can be improved with the enclosure for those who want to put in the effort.