That is unfortunately a limitation of the CCL system. If you want hot launch, you have to accept a reduced cell width (or diameter?) and if you want cold launch you have to accept a reduced cell length. I believe the internal width of a Mark 41 cell is 0.65m, of which Tomahawk the largest type round takes up the entire space of the cell, leaving you 0.1m on each side for exhaust venting if the PLAN wants a similarly-sized internal cell for its own purposes. I don't know if that is enough or whether a hot-launched missile would have to make due with a smaller internal cell volume. If the cell is circular you could probably get away with corner-only venting but then this configuration precludes quad-packing. Whatever the case, it is readily apparent that a wide variety of cell types would have to have been developed to support the various missile systems that are potentially being used.
I believe the "tubes" are square. I've read that the CCL can use corner venting and obviously only circlulsr tubes lack corners, thus squares. This quad packing doesn't become an issue.
Now, you point out that fitting a larger missile like tomahawk will limit the cell's exhaust volume, yes that is true. However is believe that larger missiles will be cold launcher instead, meaning they can fit missiles as large as the 0.85m cell width.
Of course, you mention that cold launch requires the addition of a piston to propel the missile out, however considering even HQ-9 has such a piston only 50cm long, even if we double that and cut out 1m out of the 9m length for the strike length CCL cell, that is still 8m left for missile length, and more importantly such a missile can take up the full 0.85m width/diameter of the cell.
Obviously the piston itself will vary in length considering how heavy the missile being driven is, but the key point is that cold launch allows the CCL VLS to take advantage of it's large cell width to launch missiles which smaller hot launch VLS like Mk-41 or Mk-57 cannot.
And totoro makes a good point because knowing all this we have to wonder whether hot launch is really needed.
As for space inefficiency, we can see it in differing ways.
The CCL VLS has individually larger cells and we know its hot launch will be limited by missile diameter (and thus in turn the venting volume left). However in return for that it has greater individual cell width and can easily accommodate cold launch missiles, and even the heaviest of such missiles would only result in a modest "decrease" in effective cell length resulting from the addition of a piston (however note that a realistic piston length will still leave a longer cell than most others in the world, and more than enough for virtually anything short of an IRBM)
Traditional hot launch VLS has individually smaller cells and a common exhaust venting system. Such a system is only limited by the cell width and the exhaust which the common exhaust can endure. No cell length reduction is present but even they are shorter than the PLANs CCL VLS in the first place.
Realizing all this, if we try to imagine a hot launch VLS that can do wha the CCL VLS can so -- namely an 8 cell module that launch missiles up to 0.85m diameter -- the result will be something larger than the current CCL VLS because it would necessitate a massive common exhaust system, therefore it's deck floor print and thus overall volume will be much larger than the CCL VLS.
So ultimately I would argue that a CCL VLS is more space efficient in launching larger missiles because the PLANs CCL VLS is designed for both hot and cold launch with minimal reduction in effective cell volume.
