Regardless of whether it's round, it will certainly be MUCH larger in size than a canister for YJ-18 given its quadruple air intakes. I suspect it will be fairly obviously if and when we finally do see a YJ-12 canister that it is in fact a YJ-12 canister.
I agree that a YJ-12 canister is likely to be much larger than a YJ-18 canister.
The problem is I don't think we yet know what a YJ-18 canister looks like and how large it is to be able to compare with how big a potential YJ-12 canister may be.