I don't know where you got that from. It's clear looking at Yuan vs Song that Yuan's inner hull is wider and allows for more noise reduction measure to be installed. I don't know how you can say it doesn't mean much.
I was speaking in terms of hull shaping.
But even external dimensions aren't necessarily representative, given the same space in a newer sub can use newer and more effective noise reduction methods than an older one. That said there is obviously a limit to how much noise can be reduced in a smaller versus a larger sub, but for the purposes of sensible comparisons of boats with near similar dimensions (eg kilo vs yuan vs soryu), it will be their internals that count.
An extreme example is comparing a mini sub with an SSN, which would be ridiculous.
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