At the moment this is all new to me, so I don't have answers to difficult questions (yet ... ). But when making splits or introducing nucs etc., Dadant recommends the use of a partition board to adjust the volume and thus the comb size available.
Perhaps I ought to explain how I came across this recent 'discovery': many years ago I built a 4ft KTBH, only to quickly discover that top-bar beekeeping wasn't for me. Now I hate waste, and so a couple of years back I decided that, rather than put it on the bonfire, I'd convert said KTBH into a straight-sided framed Long Hive. Purely by chance, it evolved into a 12" deep box and, just as your Deeps are 9", so are ours (they're just a little shorter than Langs). So I ended up making an Xtra-Deep (12") Dual Long Hive.
I duly 'stored' a couple of colonies in it which weren't very impressive, whilst they awaited re-queening. But - when I next looked in that hive, both colonies had exploded. And by 'exploded' I mean they had filled combs wall-to-wall and top to bottom with brood. Now to see such a huge slab of brood is truly awesome. On the next frame the same. Then a frame of drones - again, top to bottom and wall-to-wall. Same with a pollen frame and exactly the same with a honey comb. None of your oval brood patterns with a crescent-shaped arc of pollen over, and the top corners built-out thick with honey ... for some strange reason the extra 3" had changed their behaviour completely.
I have since created two more 14x12 (12" deep) colonies, and they are behaving in exactly the same way. Four colonies, each of which is powerful beyond belief when compared with every other colony on this site.
Then, during an email exchange with a friend on the South Coast of England who runs Dadants, I mentioned this unusual behaviour in passing. He replied that what I had described is exactly what he sees with his Modified Dadant hives - so this is not a fluke, it's got something to do with comb size, and I'm as puzzled as anyone as to why a few extra inches of comb should make such a difference to a colony's behaviour.
It seems to me that the Dadant concept is similar in principle to other fixed-volume hives, insomuch as there is just one brood chamber, the volume of which never changes.
Well, I'm so intrigued by this that I've already started building a set of 14"x14" Xtra-Xtra-Deep frames for one of my British Nationals, which will then fit into a Brood Box over a Super (the so-called 'Brood and a Half' configuration, which normally employs two frames) but using single frames instead as Dadant recommends. It's just an experiment at this stage, just to see what results.