Most reference speakers, in the bass/mid-bass area are mid 6-10 mm at the most on Xmax, and higher sensitivity. If they even address sub at all, other than to roll it off sooner..
Better idea..
Monitors can't do it all well..
Full range speakers are full range speakers, doesn't mean it's a good idea..or that they do it very well.. I cut anything to do with the monitor at 40, no matter.. the set up.. Small monitors (bookshelf type stuff) and no sub.. Just easy on the ol ears that way.. Higher when we add separate subs. maybe 60-80 on the roll off.
Depends on HOW they have it set up.. Biamp able, I disconnect the bass. My bass/sub system is ALWAYS better. 300 hz and down..
Can't put everything in the same box, it can't work.. :-)
BTW every inch counts.. that's X 2 there is a back side of the bass drivers too. Can't just dismiss that... Passive radiators, and ports, make NOISE.. all part of the measurement process.
IB (no port) maybe not, at first, anyways.. The enclosure might.. Depends who made it and how well it's dampened. Panels breaks, are number one in IB structures...
Regards