Its not terribly wide. There were prior images which show that even the hot launch cells do not use the corners of the cell to vent out. Instead there is a thin outer ring used for venting, and inside is the circle with the missile, which is also circular. That means the missile body itself has to have a meaningfully smaller diameter as it has to also pack folded fins somewhere. If the inner cell were rectangular, there would be extra space in the corners for fins, even if they are partly folded.
So the max inner diameter of missile that is hot launched is actually not much bigger than the ajk16 or mk41. I know that sounds like a wild, hot take, but feel free to measure it yourself. At least the cold launched missiles, without that exhaust ring, should have some more clearance and should be able to pack wider missiles.
The whole VLS design is, frankly, a bit of a head scratcher. I am sure there were limitations that made it the way it is - but it's not terribly space efficient when final missile body diameter is taken into account, at least when it comes to hot launched missiles.
We do know that the YJ-18A and CJ-10 (and maybe YJ-18C?) are hot-launched, which means that a thinner outer ring spacing inside the 850mm UVLS cells that must be included in order to act as an exhaust channel for the missile booster's hot exhaust to vent through during the missile's launch from the cell.
On the other hand, we do know that the YJ-20 and HHQ-9/A/B?/C? (+ most likely YJ-17 as well) are cold-launched, meaning that they will be ejected out of the UVLS cell using stored compressed gas before igniting their boosters after clearing the UVLS cell. This negates the need for an exhaust channel, meaning that a larger amount of volume inside the UVLS cells can go to the missiles. This is also why we see the boosters on the YJ-17 and YJ-20 are about 0.7X to 0.8 meters in diameter.
So, yes, this is indeed one notable tradeoff for using the hot-launch method in the 850mm UVLS cells, since they don't feature any exclusive (shared) exhaust channels found on hot-launch only VLS cells like those found on the 054A/B FFGs and the post-MLUed "FFG leaders". I'd wager that either the designers and engineers working on the 850mm UVLS cells back then didn't manage to figure out how to make both compressed gas for cold launch + exhaust channels for hot launch to work effectively within one system; or that they've deemed that the complexity, risks and challenges involved aren't worth the added/upgraded capability offered by such system.
Engineering is full of balances and compromises, after all.
Speaking of which, this reminds me of the claim on the quadpack SAM on the 054A FFGs:
Placard on CNS Fuyang about its VLS, showing a "missile". Ayi says this is hinting at quad packing (on the 054A?)
We do know that the 650mm VLS cells on the 054A/B FFGs are hot-launch only, and these VLS cells do have shared exhaust channels that aren't counted as part of the VLS cell volume itself.
Therefore, should the claim of this quad-packed SAM already in service on PLAN FFGs be factual - I do believe that it could/might be plausible for this quad-packed SAM to be able to be fielded in both the 650mm VLS cells on PLAN FFGs (+ FFG leaders) and in the 850mm UVLS cells on PLAN DDGs, with the latter likely leaving sufficient remainder volume inside the UVLS cells to be dedicated for exhaust channels for these quad-packed SAMs.
Of course, this part is more of a speculative deduction on my part.
