The Wolverine BOLT isn't really a perfectly volumed setup as it's somewhat loud in a 430mm configuration, but it's comparable to a 430mm springer at about the same power with heavy BBs, just without the mechanical noise. With the BOLT there's pretty much no mechanical noise besides the solenoid clicking and a valve thing whacking backward and forward, but that's really no louder than a VSR-10 trigger. But with the lack of mechanical noise, you're able to make the gun relatively quiet even at 3J with a suppressor, and at 2J and below the thing gets really really really quiet, like it's hard to tell you're shooting it even.
For voluming, you can under volume a gun and it will still be loud at the muzzle, so I believe there is more to it. Voluming is strictly based off of power, as it doesn't make sense to have a barrel so long it kills power, and it isn't great to have a barrel so short you lose power either. Even if you're perfectly volumed you're still probably having air exit, but that air just won't be able to be used for much of anything in a longer setup. It sort of sounds like it was mentioned that the air inside the barrel in front of the BB could play a part, which I'd bet it does. I think this has been mentioned in real firearms before, but never really much effort went into it as there's no way of changing it really. One point of interest is that smaller calibers suppress better than large calibers, even at about the same power. I'm not sure if it's gunpowder/gas volume, barrel volume, or there being something with larger suppressor holes, but it's a known thing that weak .45 ACP is louder than subsonic 9mm of a similar power in suppressors suited for that caliber. I'd be interested in knowing exactly why, but I'm sure it's one or many of the things I listed.
I have sort of reached the point in the hobby where all I do is split hairs, but it's really more fun than struggling to do basic things and having a bad time at the field with a busted gun. If you're new or don't care that much, you can call it good, but if you've run out of things to do then you may as well try and perfect things.
As for putting a wrap or rag in my guns, I weigh the pros and cons of that added weight, as while I could put $75 of Dynamat over my whole gun, it would very likely double it's weight and probably not reach my expectations. I'll maybe experiment with putting stuff on my outer barrel and receiver, but other than that I think it's unnecessary in a BOLT gun as there's really not much happening anywhere else.